foo.cc: In function 'int main()':
foo.cc:20:13: error: 'total' was not declared in this scope
     cout << total<< endl;
             ^~~~~
foo.cc:20:13: note: suggested alternative: 'strtol'
     cout << total<< endl;
             ^~~~~
             strtol

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