#include <bits/stdc++.h> using namespace std; int main() { int a, b, c, d, x, y; cin >> a >> b >> c >> d; x = a-c; if(x<0) { x = -x; } y = b-d; if(y<0) { y= -y; } if(x >= y) { cout << x << endl; } else { cout << y << endl; } return 0; }