#include <bits/stdc++.h>
using namespace std;
int main() {
int x1, y1, x2, y2;
scanf ("%d %d %d %d", &x1, &y1, &x2, &y2);
int x3=x1-x2;
int y3=y1-y2;
if(x3<0){
x3=-x3;
}
if(y3<0){
y3=-y3;
}
printf("%d", x3+y3);
return 0;
}
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