#include <bits/stdc++.h>
#define rep(i, n) for (int i = 0; i < (n); i++)
#define fr(i, a, b) for (int i = (a); i < (b); i++)
#define all(c) (c).begin(), (c).end()
using namespace std;
typedef long long ll;
const ll inf = 1e9;
const ll mod = 1e9 + 7;

int x, y;
int x2, y2;

int onseg(ll x1, ll y1, ll x2, ll y2) {
    x2 -= x1;
    y2 -= y1;
    x1 *= -1;
    y1 *= -1;
    if (x1 * y2 - y1 * x2 != 0) return false;
    if (x1 * x2 + y1 * y2 < 0) return false;
    if (x1 * x1 + y1 * y1 < x2 * x2 + y2 * y2) return false;

    return true;
}

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

    int ans = 0;

    if (abs(x) == 0 && abs(y) == 0) {
        ans = 0;
    } else if (abs(x) == abs(y)) {
        ans = abs(x);
        if (onseg(x, y, x2, y2)) {
            ans++; 
        }
    } else if (abs(x) == 0) {
        ans = abs(y);
    } else if (abs(y) == 0) {
        ans = abs(x);
    } else {
        ans = min(abs(x) + abs(y - x), abs(y) + abs(y - x));
    }

    cout << ans << endl;
}