/in/foo.cc:4:7: error: 'n' was not declared in this scope
    4 | int f(n){
      |       ^
/in/foo.cc: In function 'int main()':
/in/foo.cc:14:12: error: 'f' cannot be used as a function
   14 |   cout<<f(P)%(2^K)<<endl;
      |            ^