foo.cc: In function 'int main()':
foo.cc:5:5: error: 'cin' was not declared in this scope
    5 |     cin >> n;
      |     ^~~
foo.cc:5:12: error: 'n' was not declared in this scope
    5 |     cin >> n;
      |            ^
foo.cc:6:9: error: 'm' was not declared in this scope
    6 |  cin >> m;
      |         ^
foo.cc:7:2: error: 'cout' was not declared in this scope
    7 |  cout << n << m;
      |  ^~~~

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