#include<iostream>

using namespace std;

int main(){
    int a,b,c,d;

    cin >> a >> b ;
    cin >> c >> d ;

    cout << (a*d) - (c*b);

    return 0;
}
#include<iostream>
#include<string>
#include<cmath>
using namespace std;
long long int R,X,Y,ans,p;
double q;
int main(){
	cin>>R>>X>>Y;
  	p=sqrt(X*X+Y*Y)/R;
  	if(R*p!=sqrt(X*X+Y*Y))p++;
    if(p==1){
      	if(sqrt(X*X+Y*Y)!=R)p++;
    }
  	
  
  	cout<<p<<endl;
}
