ruby, 27 bytes

Result

WA

Duration

1044ms

Code [DL]

p$_[~/(.)\1 /||4]while gets

stdin

766 664
461 852
911 517
878 883
366 563
231 732
422 228
392 923
988 979
572 252
977 226
357 272
837 879
969 698
786 681
511 677
258 766
133 443
891 193
369 662
638 712
389 782
751 118
122 256
622 288
875 534
194 994
641 463
684 663
565 995
944 832
619 163

stdout

"6"
"8"
"1"
"8"
"6"
"7"
"2"
"9"
"8"
"2"
"7"
"2"
"8"
"6"
"6"
"1"
"7"
"3"
"1"
"6"
"7"
"7"
"1"
"2"
"2"
"5"
"9"
"4"
"6"
"9"
"4"
"1"

stderr

strace

10    execve("/bin/sh", ["/bin/sh", "/root/script", "/volume/CODE"], 0x7ffe2aa2a560 /* 9 vars */) = 0
11    execve("/bin/cat", ["cat", "-"], 0x556b4f4ccd40 /* 9 vars */) = 0
12    execve("/usr/local/ruby-2.7.1/bin/ruby", ["/usr/local/ruby-2.7.1/bin/ruby", "/volume/CODE"], 0x556b4f4ccd60 /* 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    +++ exited with 0 +++
10    --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=12, si_uid=0, si_status=0, si_utime=4, si_stime=1} ---
10    +++ exited with 0 +++