/in/foo.cc:35:2: error: #endif without #if
 #endif
  ^~~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:20:1: error: incomplete type 'std::ios {aka std::basic_ios<char>}' used in nested name specifier
 ios::sync_with_stdio(false);
 ^~~
/in/foo.cc:23:1: error: 'cin' was not declared in this scope
 cin>>n;
 ^~~
/in/foo.cc:32:1: error: 'cout' was not declared in this scope
 cout<<ans;
 ^~~~