#include <bits/stdc++.h>
using namespace std;
#define rep(i,a,b) for(int i=a;i<b;i++)
#define INF INT_MAX/2

int dx[8] = { -1, 0, 1, -1, 1, -1, 0, 1 };
int dy[8] = { 1, 1, 1, 0, 0, -1, -1, -1 };

int main()
{
	int x, y; cin >> x >> y;
	int x2, y2; cin >> x2 >> y2;

	int d1 = max(x2, y2) + max(abs(x - x2), abs(y - y2));
	int d2 = max(x, y);
	if (d2 < d1)
	{
		cout << d2 << endl;
		return 0;
	}

	int ans = INF;
	rep(i, 0, 8)
	{
		int xx = x2 + dx[i];
		int yy = y2 + dy[i];

		d1 = max(xx, yy) + max(abs(x - xx), abs(y - yy));
		ans = min(ans, d1);
	}
	cout << ans << endl;
}