#include<iostream>
using namespace std;
int main(){
int x1, y1, x2, y2;
cin >> x1 >> y1 >> x2 >> y2;
cout << max(abs(x1-x2), abs(y1-y2));
return 0;
}

#include<iostream>
using namespace std;
int main(){
    short x1, y1, x2, y2;
    cin >> x1 >> y1 >> x2 >> y2;
    cout << max(abs(x1-x2), abs(y1-y2));
    return 0;
}