text: #include <iostream>
  #include <iomanip>
  
  using namespace std;
  
  int main()
  {
  	double v1, v2, v3, v4, diff;
  
  	cin >> v1;
  	cin >> v2;
  	cin >> v3;
  	cin >> v4;
  
  	diff = (v1*v2) - (v3*v4);
  
  	cout << "DIFERENCA = " << diff << "\n";
  
  	return 0;
  }