#include <iostream>
#include <vector>
#include <algorithm>
#include <iomanip>
using namespace std;

typedef long long LL;

LL iabs(LL n){
    if(n < 0) return -n;
    return n;
}

int main(){
    int x, y, x2, y2;
    cin >> x >> y >> x2 >> y2;
    LL ans = 0;
    ans += max(iabs(x), iabs(y));
    if(iabs(x) == iabs(y) && iabs(x2) == iabs(y2) && iabs(x) > iabs(x2) && x/y == x2/y2){
        ans += 1;
    }
    cout << ans << endl;
    return 0;
}