foo.cc: In function 'long long int solve(long long int)':
foo.cc:14:9: error: 'ans' was not declared in this scope
  return ans;
         ^~~
foo.cc:14:9: note: suggested alternative: 'ams'
  return ans;
         ^~~
         ams

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