#include <iostream>

 using namespace std;

void Rofyda_Elghadban(){
  #ifndef ONLINE_JUDGE
    freopen("input.txt", "r", stdin), freopen("output.txt", "w", stdout);
  #endif
}
 int main()
 {   Rofyda_Elghadban();
 int A ,B ,C ,D ;
 int Difference = (A*B)-(C*D);
 cin>>A >>B >>C >>D ;
 cout<<"Difference"<<" "<<"="<<" "<<(A*B)-(C*D) ;
  return 0;
 }