foo.cc: In function 'int main()':
foo.cc:6:2: error: 'cin' was not declared in this scope
  cin >> L >> M;
  ^~~
foo.cc:6:2: note: suggested alternative: 'main'
  cin >> L >> M;
  ^~~
  main
foo.cc:21:4: error: 'cout' was not declared in this scope
    cout << sum;
    ^~~~
foo.cc:24:3: error: expected '}' at end of input
   }
   ^
foo.cc:5:12: warning: unused variable 'i' [-Wunused-variable]
  int L, M, i,sum = 0;
            ^
foo.cc:24:3: error: expected '}' at end of input
   }
   ^

[Hydro](https://hydro.ac)提供评测服务