#include <bits/stdc++.h>
using namespace std;
int main() {
  int x1, y1, x2, y2;
  cin >> x1 >> y1 >> x2 >> y2;
  int a = abs(x1 - x2);
  int b = abs(y1 - y2);
  int u = min(a, b);
  cout << u + abs(a - b);
  return 0;
}
