/in/foo.cc:2:17: error: 'ad' is not a namespace-name
 using namespace ad;
                 ^~
/in/foo.cc:2:19: error: expected namespace-name before ';' token
 using namespace ad;
                   ^
/in/foo.cc: In function 'int main()':
/in/foo.cc:6:5: error: 'cin' was not declared in this scope
     cin >> a >> b;
     ^~~
/in/foo.cc:6:5: note: suggested alternative:
In file included from /usr/include/x86_64-linux-gnu/c++/6/bits/stdc++.h:75:0,
                 from /in/foo.cc:1:
/usr/include/c++/6/iostream:60:18: note:   'std::cin'
   extern istream cin;  /// Linked to standard input
                  ^~~
/in/foo.cc:7:5: error: 'cout' was not declared in this scope
     cout << a + b << endl;
     ^~~~
/in/foo.cc:7:5: note: suggested alternative:
In file included from /usr/include/x86_64-linux-gnu/c++/6/bits/stdc++.h:75:0,
                 from /in/foo.cc:1:
/usr/include/c++/6/iostream:61:18: note:   'std::cout'
   extern ostream cout;  /// Linked to standard output
                  ^~~~
/in/foo.cc:7:22: error: 'endl' was not declared in this scope
     cout << a + b << endl;
                      ^~~~
/in/foo.cc:7:22: note: suggested alternative:
In file included from /usr/include/c++/6/istream:39:0,
                 from /usr/include/c++/6/sstream:38,
                 from /usr/include/c++/6/complex:45,
                 from /usr/include/c++/6/ccomplex:39,
                 from /usr/include/x86_64-linux-gnu/c++/6/bits/stdc++.h:52,
                 from /in/foo.cc:1:
/usr/include/c++/6/ostream:590:5: note:   'std::endl'
     endl(basic_ostream<_CharT, _Traits>& __os)
     ^~~~