foo.cc:2:7: error: expected nested-name-specifier before 'namesapce'
    2 | using namesapce std;
      |       ^~~~~~~~~
foo.cc: In function 'int main()':
foo.cc:5:1: error: 'ios' has not been declared
    5 | ios::sync_with_stdio(0);
      | ^~~
foo.cc:6:1: error: 'cin' was not declared in this scope; did you mean 'std::cin'?
    6 | cin>>a>>b;
      | ^~~
      | std::cin
In file included from foo.cc:1:
/usr/include/c++/9/iostream:60:18: note: 'std::cin' declared here
   60 |   extern istream cin;  /// Linked to standard input
      |                  ^~~
foo.cc:7:1: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
    7 | cout<<a+b-b+b-b+b;
      | ^~~~
      | std::cout
In file included from foo.cc:1:
/usr/include/c++/9/iostream:61:18: note: 'std::cout' declared here
   61 |   extern ostream cout;  /// Linked to standard output
      |                  ^~~~

[Hydro](https://hydro.ac)提供评测服务