node, 51 bytes

Result

AC

Code [DL]

(q=require("fs")).write(1,q.readFileSync(0).sort())

stdin

2453903931685142362603498780620599231357604368880812282361909148626802089784731364386541019669558477

stdout

0000000000111111111222222222233333333333344444444455555556666666666666777777888888888888889999999999

stderr

(node:5) DeprecationWarning: Calling an asynchronous function without callback is deprecated.

strace