perl, 22 bytes

Result

WA

Duration

783ms

Code [DL]

/(.) ?\1/,print$1for<>

stdin

599 997
853 315
264 667
628 828
241 434
911 228
638 368
311 414
679 993
371 413
655 618
793 386
896 871
674 747
443 557
785 884
198 788
962 623
644 443
816 299
511 793
833 387
933 392
794 491
611 775
672 717
135 553
638 359
244 647
446 744
871 996
128 122

stdout

93688111995333488849133411554492

stderr

strace

12    execve("/bin/sh", ["/bin/sh", "/root/script", "/volume/CODE"], 0x7ffc0bb6bef0 /* 7 vars */) = 0
13    execve("/bin/cat", ["cat", "-"], 0x56452dc03d30 /* 7 vars */) = 0
14    execve("/usr/bin/perl", ["/usr/bin/perl", "/volume/CODE"], 0x56452dc03d40 /* 7 vars */) = 0
13    +++ exited with 0 +++
12    --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=13, si_uid=0, si_status=0, si_utime=0, si_stime=0} ---
14    +++ exited with 0 +++
12    --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=14, si_uid=0, si_status=0, si_utime=0, si_stime=0} ---
12    +++ exited with 0 +++