foo.cc: In function 'int main()':
foo.cc:16:9: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
   16 |         cout<<ans;
      |         ^~~~
      |         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
      |                  ^~~~

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