wren, 83 bytes

Result

WA

Duration

887ms

Code [DL]

import"io"for Stdin
while(1)var s=Stdin.readLine()&&System.print(s[s[1]!=s[2]?4:2])

stdin

981 685
289 828
482 117
994 414
644 554
418 772
833 595
122 253
844 798
181 812
711 618
272 224
573 772
618 812
799 996
461 865
486 887
155 554
231 682
195 953
988 588
125 528
911 181
855 441
629 688
224 642
127 247
879 496
147 716
897 655
895 559
819 116

stdout

stderr

[/volume/CODE line 2] Error at 'var': Expected expression.
[/volume/CODE line 2] Error at 's': Expect end of file.

strace

11    execve("/bin/sh", ["/bin/sh", "/root/script", "/volume/CODE"], 0x7ffd034c7e70 /* 9 vars */) = 0
12    execve("/bin/cat", ["cat", "-"], 0x557ba9b6cd30 /* 9 vars */) = 0
13    execve("/root/wren", ["/root/wren", "/volume/CODE"], 0x557ba9b6cd40 /* 9 vars */ <unfinished ...>
12    +++ exited with 0 +++
11    --- 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 resumed>)             = 0
13    +++ exited with 65 +++
11    --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=13, si_uid=0, si_status=65, si_utime=0, si_stime=0} ---
11    +++ exited with 65 +++