#include <algorithm>
#include <cstdio>
#include <iostream>
#include <map>
#include <math.h>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <vector>
using namespace std;

#define ll long long
#define INF (1 << 30)
#define INFLL (1LL << 60)

int main() {
	int x1,x2,y1,y2;
	cin >> x1 >> y1;
	cin >> x2 >> y2;
	if(x2 < x1 && y2 < y1 && x1 > 0 && y1 > 0 && x1 == y1 && x2 == y2) cout << max(x1,y1) + 1 << endl;
	else if(x2 > x1 && y2 > y1 && x1 < 0 && y1 < 0 && x1 == y1 && x2 == y2) cout << max(-x1,-y1) + 1 << endl;
	else if(x2 < x1 && y2 > y1 && x1 > 0 && y1 < 0 && x1 == -y1 && x2 == -y2) cout << max(x1,y1) + 1 << endl;
	else if(x2 > x1 && y2 < y1 && x1 < 0 && y1 > 0 && -x1 == y1 && -x2 == y2) cout << max(x1,y1) + 1 << endl;
	else cout << max(abs(x1),abs(y1)) << endl;
	return 0;
}