ruby, 34 bytes

Result

AC

Duration

969ms

Code [DL]

$<.map{puts _1=~/(.)\1 /?$1:_1[4]}

stdin

244 224
219 996
725 727
856 557
948 884
473 447
255 379
955 667
267 582
355 354
113 836
176 761
433 564
633 339
361 471
486 463
677 762
845 549
733 332
782 779
454 156
439 357
753 319
232 332
299 941
467 695
977 179
285 972
932 322
164 433
764 477
524 429

stdout

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

stderr

strace

10    execve("/bin/sh", ["/bin/sh", "/root/script", "/volume/CODE"], 0x7ffd56368ce0 /* 9 vars */) = 0
11    execve("/bin/cat", ["cat", "-"], 0x55df99e28d40 /* 9 vars */) = 0
12    execve("/usr/local/ruby-2.7.1/bin/ruby", ["/usr/local/ruby-2.7.1/bin/ruby", "/volume/CODE"], 0x55df99e28d60 /* 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=5, si_stime=2} ---
10    +++ exited with 0 +++