#define _USE_MATH_DEFINES
#include <algorithm>
#include <cstdio>
#include <functional>
#include <iostream>
#include <cfloat>
#include <climits>
#include <cstring>
#include <cmath>
#include <map>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <time.h>
#include <vector>
using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> i_i;
typedef pair<ll, int> ll_i;
typedef pair<double, int> d_i;
typedef pair<ll, ll> ll_ll;
typedef pair<double, double> d_d;
struct edge { int u, v; ll w; };

ll MOD = 1000000007;
ll _MOD = 1000000009;
double EPS = 1e-10;

int main() {
	int x, y, x2, y2;
	cin >> x >> y >> x2 >> y2;
	if (abs(x) == abs(y) && abs(x2) == abs(y2) && x/abs(x) == x2/abs(x2) && abs(y)/y == abs(y2)/y2 && (ll)x*x+(ll)y*y > (ll)x2*x2+(ll)y2*y2)
		cout << max(abs(x), abs(y)) + 1 << endl;
	else
		cout << max(abs(x), abs(y)) << endl;
}