foo.cc: In function 'int main()':
foo.cc:6:9: error: 'cin' was not declared in this scope; did you mean 'std::cin'?
    6 |         cin>>a' '>>b' '>>c' ';
      |         ^~~
      |         std::cin
iostream:60:18: note: 'std::cin' declared here
foo.cc:8:9: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
    8 |         cout<<d;
      |         ^~~~
      |         std::cout
iostream:61:18: note: 'std::cout' declared here

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