foo.cc:23:9: warning: missing terminating " character
  printf("%lld\n', ans);
         ^
foo.cc:23:9: error: missing terminating " character
  printf("%lld\n', ans);
         ^~~~~~~~~~~~~~~
foo.cc: In function 'int main()':
foo.cc:24:2: error: expected primary-expression before 'return'
  return 0;
  ^~~~~~

自豪的采用 HydroJudge 进行评测(github.com/hydro-dev/HydroJudge)