answer.code: In function ‘long long int calc()’:
answer.code:37:1: warning: no return statement in function returning non-void [-Wreturn-type]
   37 | }
      | ^
answer.code: In function ‘int main()’:
answer.code:75:15: error: ‘res’ was not declared in this scope
   75 |         cout<<res<<endl;
      |               ^~~