bash-pure, 60 bytes

Result

WA

Code [DL]

while read -n1 c;do a[c]+=$c;done
echo $(IFS=;echo"${a[*]}")

stdin

6269364885884681782659131763274115106614613507609374480574336625054499262199980224509406695768937767

stdout

stderr

/bin/bash: warning: setlocale: LC_ALL: cannot change locale (en_US.UTF-8)
/code.bash: line 2: echo0000000011111111122222222333333334444444444455555555566666666666666666777777777788888888899999999999: command not found

strace