wren, 85 bytes

Result

WA

Duration

860ms

Code [DL]

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

stdin

159 595
922 233
259 559
755 331
118 611
381 181
711 279
765 658
828 592
618 148
184 867
829 713
766 659
519 939
966 661
171 223
952 726
622 126
584 889
784 338
529 723
633 537
611 331
771 117
978 875
667 774
829 569
133 428
797 738
929 264
452 324
911 118

stdout

stderr

Null does not implement '[_]'.
[/volume/CODE line 3] in (script)

strace

12    execve("/bin/sh", ["/bin/sh", "/root/script", "/volume/CODE"], 0x7ffd7e99e260 /* 9 vars */) = 0
13    execve("/bin/cat", ["cat", "-"], 0x55c06842cd30 /* 9 vars */) = 0
14    execve("/root/wren", ["/root/wren", "/volume/CODE"], 0x55c06842cd40 /* 9 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 +++