foo.cc: In function 'int main()':
foo.cc:6:2: error: 'cin' was not declared in this scope; did you mean 'std::cin'?
    6 |  cin >> u >> m >> f;
      |  ^~~
      |  std::cin
In file included from /usr/include/x86_64-linux-gnu/c++/9/bits/stdc++.h:75,
                 from foo.cc:1:
/usr/include/c++/9/iostream:60:18: note: 'std::cin' declared here
   60 |   extern istream cin;  /// Linked to standard input
      |                  ^~~
foo.cc:7:2: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
    7 |  cout << u * 0.2 + m * 0.2 + f * 0.6 << endl;
      |  ^~~~
      |  std::cout
In file included from /usr/include/x86_64-linux-gnu/c++/9/bits/stdc++.h:75,
                 from foo.cc:1:
/usr/include/c++/9/iostream:61:18: note: 'std::cout' declared here
   61 |   extern ostream cout;  /// Linked to standard output
      |                  ^~~~
foo.cc:7:41: error: 'endl' was not declared in this scope; did you mean 'std::endl'?
    7 |  cout << u * 0.2 + m * 0.2 + f * 0.6 << endl;
      |                                         ^~~~
      |                                         std::endl
In file included from /usr/include/c++/9/istream:39,
                 from /usr/include/c++/9/sstream:38,
                 from /usr/include/c++/9/complex:45,
                 from /usr/include/c++/9/ccomplex:39,
                 from /usr/include/x86_64-linux-gnu/c++/9/bits/stdc++.h:54,
                 from foo.cc:1:
/usr/include/c++/9/ostream:599:5: note: 'std::endl' declared here
  599 |     endl(basic_ostream<_CharT, _Traits>& __os)
      |     ^~~~

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