golang, 101 bytes

Result

WA

Duration

1606ms

Code [DL]

package main;import."fmt";func main(){for{s,t:="","";Scan(&s,&t);Print((s+t)[3+1/ ^(s[1]^s[2])]&15)}}

stdin

386 698
419 115
413 126
735 457
678 365
459 256
988 854
577 774
911 164
946 115
423 577
967 779
547 272
225 522
488 993
569 423
344 796
419 134
636 634
371 715
911 616
254 776
377 778
668 686
565 558
757 577
455 299
788 558
684 884
276 698
979 279
711 313

stdout

61143287115725947167677655258623

stderr

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

goroutine 1 [running]:
main.main()
	/tmp/code.go:1 +0x263

strace

11    execve("/bin/sh", ["/bin/sh", "/root/script", "/volume/CODE"], 0x7ffd611939c0 /* 7 vars */) = 0
12    execve("/usr/bin/realpath", ["realpath", "/volume/CODE"], 0x559ce357cd18 /* 7 vars */) = 0
12    +++ exited with 0 +++
11    --- 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("/bin/ln", ["ln", "-sf", "/volume/CODE", "/tmp/code.go"], 0x559ce357cd38 /* 7 vars */) = 0
13    +++ exited with 0 +++
11    --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=13, si_uid=0, si_status=0, si_utime=0, si_stime=0} ---
14    execve("/usr/bin/go", ["/usr/bin/go", "build", "-o", "/tmp/code", "/tmp/code.go"], 0x559ce3d8a028 /* 7 vars */) = 0
22    execve("/usr/lib/go/pkg/tool/linux_amd64/compile", ["/usr/lib/go/pkg/tool/linux_amd64"..., "-V=full"], 0xc000488f70 /* 25 vars */) = 0
23    execve("/usr/lib/go/pkg/tool/linux_amd64/compile", ["/usr/lib/go/pkg/tool/linux_amd64"..., "-V=full"], 0xc00011d450 /* 25 vars */) = 0
26    +++ exited with 0 +++
24    +++ exited with 0 +++
27    +++ exited with 0 +++
25    +++ exited with 0 +++
22    +++ exited with 0 +++
16    --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=22, si_uid=0, si_status=0, si_utime=0, si_stime=0} ---
29    +++ exited with 0 +++
30    +++ exited with 0 +++
31    +++ exited with 0 +++
23    +++ exited with 0 +++
16    --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=23, si_uid=0, si_status=0, si_utime=0, si_stime=0} ---
28    execve("/usr/lib/go/pkg/tool/linux_amd64/asm", ["/usr/lib/go/pkg/tool/linux_amd64"..., "-V=full"], 0xc000489110 /* 25 vars */) = 0
32    execve("/usr/lib/go/pkg/tool/linux_amd64/asm", ["/usr/lib/go/pkg/tool/linux_amd64"..., "-V=full"], 0xc00011d6c0 /* 25 vars */) = 0
33    +++ exited with 0 +++
34    +++ exited with 0 +++
35    +++ exited with 0 +++
36    +++ exited with 0 +++
28    +++ exited with 0 +++
21    --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=28, si_uid=0, si_status=0, si_utime=0, si_stime=0} ---
38    +++ exited with 0 +++
37    +++ exited with 0 +++
39    +++ exited with 0 +++
32    +++ exited with 0 +++
19    --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=32, 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-build475010354/b001/_pkg"..., "-trimpath", "/tmp/go-build475010354/b001=>", "-p", "main", "-complete", "-buildid", "TA9AnfdaHvsTCRAWBHz9/TA9AnfdaHvs"..., "-goversion", "go1.13.10", "-D", "_/tmp", "-importcfg", "/tmp/go-build475010354/b001/impo"..., "-pack", "-c=2", "/tmp/code.go"], 0xc0003464e0 /* 25 vars */) = 0
43    +++ exited with 0 +++
44    +++ exited with 0 +++
42    +++ exited with 0 +++
41    +++ exited with 0 +++
40    +++ exited with 0 +++
16    --- 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"], 0xc0003468f0 /* 25 vars */) = 0
49    +++ exited with 0 +++
47    +++ exited with 0 +++
48    +++ exited with 0 +++
46    +++ exited with 0 +++
45    +++ exited with 0 +++
19    --- 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-build475010354/b001/exe/"..., "-importcfg", "/tmp/go-build475010354/b001/impo"..., "-buildmode=exe", "-buildid=fTdaFOqYoX2Q-hBxtx2L/TA"..., "-extld=gcc", "/tmp/go-build475010354/b001/_pkg"...], 0xc000346d00 /* 25 vars */) = 0
54    +++ exited with 0 +++
52    +++ exited with 0 +++
53    +++ exited with 0 +++
51    +++ exited with 0 +++
50    +++ exited with 0 +++
19    --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=50, si_uid=0, si_status=0, si_utime=19, si_stime=5} ---
20    +++ exited with 0 +++
21    +++ exited with 0 +++
19    +++ exited with 0 +++
18    +++ exited with 0 +++
17    +++ exited with 0 +++
16    +++ exited with 0 +++
15    +++ exited with 0 +++
14    +++ exited with 0 +++
11    --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=14, si_uid=0, si_status=0, si_utime=5, si_stime=12} ---
55    execve("/bin/cat", ["cat", "-"], 0x559ce357cd08 /* 7 vars */) = 0
56    execve("/tmp/code", ["/tmp/code"], 0x559ce357ccf0 /* 7 vars */) = 0
55    +++ exited with 0 +++
11    --- 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 +++
11    --- 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"], 0x559ce357ccf0 /* 7 vars */) = 0
61    +++ exited with 0 +++
11    --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=61, si_uid=0, si_status=0, si_utime=0, si_stime=0} ---
11    +++ exited with 0 +++