#include <iostream>
using namespace std;

int addition (int a, int b){ return a+b; }
int subtraction (int a, int b){ return a-b; }

int operation (int x, int y, int (*functioncall)(int,int)){
  int r = (*functioncall)(x,y);
  return r;
}

int main(){
  int m,n;
  int (*sub_ptr)(int,int) = subtraction;

  m = operation (7, 5, addition);
  n = operation (20, m, sub_ptr);
  cout << "Result: " << n << endl;
  return 0;
}