rail, 52 bytes

Result

WA

Code [DL]

$ ':'
 \
  \-(!a!)(a)(a)#

$ 'main'
 \
  \-[x]{:}oo#

stdin

4576816428181040684660791544628220994115314665966895027333827334474384337920485783426193189750893550

stdout

xx

stderr

strace