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

#define RREP(i,s,e) for (int i = e-1; i >= s; i--)
#define rrep(i,n) RREP(i,0,n)
#define REP(i,s,e) for (int i = s; i < e; i++)
#define rep(i,n) REP(i,0,n)

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