#include <iostream>
using namespace std;
int main(){
long long xm;
long long ym;
long long xp;
long long yp;
cin >> xm;
cin >> ym;
cin >> xp;
cin >> yp;
long long t = (xp + yp) - (xm + ym);
cout << t << endl;
}
//https://pt.stackoverflow.com/q/206373/101
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