foo.cc:5:7: error: expected nested-name-specifier before 'namesapce'
 using namesapce std;
       ^~~~~~~~~
foo.cc:6:1: error: 'stack' does not name a type; did you mean 'obstack'?
 stack<char> st;
 ^~~~~
 obstack
foo.cc:7:1: error: 'string' does not name a type; did you mean 'stdin'?
 string A,B;
 ^~~~~~
 stdin
foo.cc: In function 'int main()':
foo.cc:11:2: error: 'cin' was not declared in this scope
  cin>>A;
  ^~~
foo.cc:11:2: 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:11:7: error: 'A' was not declared in this scope
  cin>>A;
       ^
foo.cc:12:7: error: 'B' was not declared in this scope
  cin>>B;
       ^
foo.cc:17:9: error: 'st' was not declared in this scope
   while(st.top()==A[con]&&con!=-1&&!st.empty()) {con--;st.pop();}
         ^~
foo.cc:21:3: error: 'st' was not declared in this scope
   st.push(B[i]);
   ^~
foo.cc:23:2: error: 'cout' was not declared in this scope
  cout<<ANS;
  ^~~~
foo.cc:23:2: 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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