php, 61 bytes

Result

WA

Duration

799ms

Code [DL]

while($c=fgetc(STDIN))echo(1>$x=$c>S?:++$x%51-($c>J)*51)?:$c;

stdin

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    K                                             

stdout

while($c=fgetc(STDIN))echo(1>$x=$c>S?:++$x%51-($c>J)*51)?:$c;

stderr

strace

10    execve("/bin/sh", ["/bin/sh", "/root/script", "/volume/CODE"], 0x7ffcafc4c790 /* 7 vars */) = 0
11    execve("/bin/cat", ["cat", "-"], 0x55cb94300d30 /* 7 vars */ <unfinished ...>
12    execve("/usr/bin/php", ["/usr/bin/php", "/volume/CODE"], 0x55cb94300d40 /* 7 vars */ <unfinished ...>
11    <... execve resumed> )            = 0
12    <... execve resumed> )            = 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=0, si_stime=0} ---
10    +++ exited with 0 +++