vim, 29 bytes

Result

WA

Duration

838ms

Code [DL]

:%s/.*\(.\)\(\1\| \).*/\1/
ZZ

Disassembly

:%s/.*\(.\)\(\1\| \).*/\1/<NL>ZZ

stdin

415 552
361 915
585 186
736 639
665 771
813 335
155 357
956 126
422 727
541 155
323 436
187 875
232 284
976 279
838 837
559 558
144 443
755 525
652 398
371 775
668 868
944 443
577 229
841 414
637 582
975 339
266 224
288 296
988 746
385 873
737 324
411 155

stdout

5
1
5
6
7
3
5
6
2
5
3
7
2
6
8
5
4
5
2
7
8
4
2
1
7
3
2
8
8
5
7
5

stderr

strace

10    execve("/bin/sh", ["/bin/sh", "/root/script", "/volume/CODE"], 0x7ffdbe386940 /* 9 vars */) = 0
11    execve("/bin/cat", ["cat", "-"], 0x55ac09e7ad00 /* 9 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("/usr/bin/vim", ["/usr/bin/vim", "-N", "-u", "NONE", "-i", "NONE", "-s", "/volume/CODE", "/tmp/out"], 0x55ac0a49e288 /* 10 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("/bin/cat", ["cat", "/tmp/out"], 0x55ac09e7ac98 /* 9 vars */) = 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=0, si_stime=0} ---
14    execve("/bin/rm", ["rm", "/tmp/out"], 0x55ac09e7ac98 /* 9 vars */) = 0
14    +++ exited with 0 +++
10    --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=14, si_uid=0, si_status=0, si_utime=0, si_stime=0} ---
10    +++ exited with 0 +++