foo.cc:3:17: error: 'st' is not a namespace-name
 using namespace st;
                 ^~
foo.cc:3:19: error: expected namespace-name before ';' token
 using namespace st;
                   ^
foo.cc: In function 'int main()':
foo.cc:7:2: error: 'cin' was not declared in this scope
  cin>>q>>" ">>w>>" ">>e>>" ">>r>>" ">>t>>" ">>y>>" ">>u>>" ">>i>>" ">>o>>" ">>p>>" ">>a>>" ">>s>>" ">>d;
  ^~~
foo.cc:7:2: note: suggested alternative:
In file included from foo.cc:2:0:
/usr/include/c++/7/iostream:60:18: note:   'std::cin'
   extern istream cin;  /// Linked to standard input
                  ^~~
foo.cc:9:2: error: 'cout' was not declared in this scope
  cout<<"Yes";
  ^~~~
foo.cc:9:2: note: suggested alternative:
In file included from foo.cc:2:0:
/usr/include/c++/7/iostream:61:18: note:   'std::cout'
   extern ostream cout;  /// Linked to standard output
                  ^~~~
foo.cc:12:2: error: 'cout' was not declared in this scope
  cout<<"No";
  ^~~~
foo.cc:12:2: note: suggested alternative:
In file included from foo.cc:2:0:
/usr/include/c++/7/iostream:61:18: note:   'std::cout'
   extern ostream cout;  /// Linked to standard output
                  ^~~~

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