#include <cstdio>
#include <iostream>
#include <sstream>
#include <fstream>
#include <iomanip>
#include <algorithm>
#include <cmath>
#include <string>
#include <vector>
#include <list>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <bitset>
#include <numeric>
#include <limits>
#include <climits>
#include <cfloat>
#include <functional>
using namespace std;

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

    long long ans = max(x, y);
    if(abs(x) == abs(y) && abs(x2) == abs(y2) && abs(x) > abs(x2)){
        x  /= max(1, abs(x) );
        y  /= max(1, abs(y) );
        x2 /= max(1, abs(x2));
        y2 /= max(1, abs(y2));
        if(x == x2 && y == y2)
            ++ ans;
    }
    cout << ans << endl;

    return 0;
}