golang, 103 bytes

Result

AC

Duration

1541ms

Code [DL]

package main;import."fmt";func main(){for{s,t:="","";Scan(&s,&t);Print((t+s)[(s[1]^s[2]^15)/15*5]&15)}}

stdin

162 614
928 815
462 685
727 632
126 129
488 776
511 337
346 447
937 772
954 643
218 181
172 243
764 663
144 248
799 982
244 914
599 994
375 578
568 174
474 312
782 671
242 845
455 541
928 889
511 113
551 519
934 434
972 114
955 952
966 283
329 493
991 229

stdout

68661814761264949513685815415642

stderr

panic: runtime error: index out of range [1] with length 0

goroutine 1 [running]:
main.main()
	/tmp/code.go:1 +0x24c

strace

10    execve("/bin/sh", ["/bin/sh", "/root/script", "/volume/CODE"], 0x7ffe08f384e0 /* 7 vars */) = 0
11    execve("/usr/bin/realpath", ["realpath", "/volume/CODE"], 0x55ec6f660d18 /* 7 vars */) = 0
11    +++ exited with 0 +++
10    --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=11, si_uid=0, si_status=0, si_utime=0, si_stime=0} ---
12    execve("/bin/ln", ["ln", "-sf", "/volume/CODE", "/tmp/code.go"], 0x55ec6f660d38 /* 7 vars */) = 0
12    +++ exited with 0 +++
10    --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=12, si_uid=0, si_status=0, si_utime=0, si_stime=0} ---
13    execve("/usr/bin/go", ["/usr/bin/go", "build", "-o", "/tmp/code", "/tmp/code.go"], 0x55ec704dd028 /* 7 vars */) = 0
19    execve("/usr/lib/go/pkg/tool/linux_amd64/compile", ["/usr/lib/go/pkg/tool/linux_amd64"..., "-V=full"], 0xc00042aa90 /* 25 vars */) = 0
20    execve("/usr/lib/go/pkg/tool/linux_amd64/compile", ["/usr/lib/go/pkg/tool/linux_amd64"..., "-V=full"], 0xc00044b1e0 /* 25 vars */) = 0
24    +++ exited with 0 +++
25    +++ exited with 0 +++
23    +++ exited with 0 +++
20    +++ exited with 0 +++
16    --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=20, si_uid=0, si_status=0, si_utime=0, si_stime=0} ---
26    execve("/usr/lib/go/pkg/tool/linux_amd64/asm", ["/usr/lib/go/pkg/tool/linux_amd64"..., "-V=full"], 0xc0000901a0 /* 25 vars */) = 0
28    +++ exited with 0 +++
30    +++ exited with 0 +++
29    +++ exited with 0 +++
31    +++ exited with 0 +++
19    +++ exited with 0 +++
27    --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=19, si_uid=0, si_status=0, si_utime=0, si_stime=0} ---
32    ????( <unfinished ...>
34    +++ exited with 0 +++
35    +++ exited with 0 +++
33    +++ exited with 0 +++
32    +++ exited with 0 +++
26    +++ exited with 0 +++
21    --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=26, si_uid=0, si_status=0, si_utime=0, si_stime=0} ---
36    execve("/usr/lib/go/pkg/tool/linux_amd64/asm", ["/usr/lib/go/pkg/tool/linux_amd64"..., "-V=full"], 0xc00013a1a0 /* 25 vars */) = 0
38    +++ exited with 0 +++
39    +++ exited with 0 +++
37    +++ exited with 0 +++
36    +++ exited with 0 +++
14    --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=36, si_uid=0, si_status=0, si_utime=0, si_stime=0} ---
40    execve("/usr/lib/go/pkg/tool/linux_amd64/compile", ["/usr/lib/go/pkg/tool/linux_amd64"..., "-o", "/tmp/go-build446419101/b001/_pkg"..., "-trimpath", "/tmp/go-build446419101/b001=>", "-p", "main", "-complete", "-buildid", "OgQPrCAXTVQAaxlm_ehH/OgQPrCAXTVQ"..., "-goversion", "go1.13.10", "-D", "_/tmp", "-importcfg", "/tmp/go-build446419101/b001/impo"..., "-pack", "-c=2", "/tmp/code.go"], 0xc0000904e0 /* 25 vars */) = 0
43    +++ exited with 0 +++
42    +++ exited with 0 +++
44    +++ exited with 0 +++
41    +++ exited with 0 +++
40    +++ exited with 0 +++
15    --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=40, si_uid=0, si_status=0, si_utime=1, si_stime=0} ---
45    execve("/usr/lib/go/pkg/tool/linux_amd64/link", ["/usr/lib/go/pkg/tool/linux_amd64"..., "-V=full"], 0xc00013a340 /* 25 vars */) = 0
46    ????( <unfinished ...>
47    +++ exited with 0 +++
49    +++ exited with 0 +++
46    +++ exited with 0 +++
48    +++ exited with 0 +++
45    +++ exited with 0 +++
21    --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=45, si_uid=0, si_status=0, si_utime=0, si_stime=0} ---
50    execve("/usr/lib/go/pkg/tool/linux_amd64/link", ["/usr/lib/go/pkg/tool/linux_amd64"..., "-o", "/tmp/go-build446419101/b001/exe/"..., "-importcfg", "/tmp/go-build446419101/b001/impo"..., "-buildmode=exe", "-buildid=DlPCDHYU5YWXTWDbTrwn/Og"..., "-extld=gcc", "/tmp/go-build446419101/b001/_pkg"...], 0xc00013a9c0 /* 25 vars */) = 0
51    +++ exited with 0 +++
53    +++ exited with 0 +++
54    +++ exited with 0 +++
52    +++ exited with 0 +++
50    +++ exited with 0 +++
15    --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=50, si_uid=0, si_status=0, si_utime=19, si_stime=5} ---
27    +++ exited with 0 +++
22    +++ exited with 0 +++
21    +++ exited with 0 +++
18    +++ exited with 0 +++
17    +++ exited with 0 +++
16    +++ exited with 0 +++
15    +++ exited with 0 +++
14    +++ exited with 0 +++
13    +++ exited with 0 +++
10    --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=13, si_uid=0, si_status=0, si_utime=11, si_stime=9} ---
56    execve("/tmp/code", ["/tmp/code"], 0x55ec6f660cf0 /* 7 vars */ <unfinished ...>
55    execve("/bin/cat", ["cat", "-"], 0x55ec6f660d08 /* 7 vars */ <unfinished ...>
56    <... execve resumed>)             = 0
55    <... execve resumed>)             = 0
55    +++ exited with 0 +++
10    --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=55, si_uid=0, si_status=0, si_utime=0, si_stime=0} ---
57    +++ exited with 2 +++
59    +++ exited with 2 +++
60    +++ exited with 2 +++
58    +++ exited with 2 +++
56    +++ exited with 2 +++
10    --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=56, si_uid=0, si_status=2, si_utime=0, si_stime=0} ---
61    execve("/bin/rm", ["rm", "/tmp/code.go", "/tmp/code"], 0x55ec6f660cf0 /* 7 vars */) = 0
61    +++ exited with 0 +++
10    --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=61, si_uid=0, si_status=0, si_utime=0, si_stime=0} ---
10    +++ exited with 0 +++