#include <bits/stdc++.h>
using namespace std;
int main() {
  int x1, y1, x2, y2;
  cin >> x1 >> y1 >> x2 >> y2;
  int dx = abs(x1 - x2);
  int dy = abs(y1 - y2);
  int ans1 = min(dx, dy);
  if (dy > ans1)
    ans1 = dy - ans1 + ans1;
  else if (dx > ans1)
    ans1 = dx - ans1 + ans1;
  cout << ans1 << endl;
  return 0;
}
