foo.cc:2:14: error: expected '{' before ';' token
 namespace std;
              ^
foo.cc: In function 'int main()':
foo.cc:6:5: error: 'cin' was not declared in this scope
     cin>>n;
     ^~~
foo.cc:6:5: note: suggested alternative:
In file included from foo.cc:1:
/usr/lib/gcc/x86_64-alpine-linux-musl/8.3.0/../../../../include/c++/8.3.0/iostream:60:18: note:   'std::cin'
   extern istream cin;  /// Linked to standard input
                  ^~~
foo.cc:14:13: error: 'cout' was not declared in this scope
             cout<<i;
             ^~~~
foo.cc:14:13: note: suggested alternative:
In file included from foo.cc:1:
/usr/lib/gcc/x86_64-alpine-linux-musl/8.3.0/../../../../include/c++/8.3.0/iostream:61:18: note:   'std::cout'
   extern ostream cout;  /// Linked to standard output
                  ^~~~