d-gdc, 114 bytes

Result

ERROR

Code [DL]

import std.stdio;import std.array;import std.algorithm;void main(){write(join(sort!("a<b")(split(readln(),""))));}

stdin

0973497619951107164739418102788373085056281098261239471470981409324712981910419739220331871543382921

stdout

stderr

strace