include <bits/stdc++.h>

using namespace std;

int main() {

int x1, y1, x2, y2, a;
scanf("%d%d%d%d", &x1, &y1, &x2, &y2);
a = abs(x1 - x2) + abs(y1 - y2);
printf("%d", a);
return 0;

}