goruby, 11 bytes

Result

AC

Code [DL]

s$<.ch.so.j

stdin

7445660952897841431967028663120201997731701341084530258129352572871801767346234681031679980650061210

stdout

0000000000000111111111111112222222222333333333444444445555555666666666667777777777788888888899999999

stderr

<internal:golf_prelude>:14: warning: ARGF#chars is deprecated; use #each_char instead

strace