#include <iostream>
#include <cmath>
using namespace std;

int gcd(int a, int b) {
    while (b != 0) {
        int temp = b;
        b = a % b;
        a = temp;
    }
    return a;
}

int main() {
    int x1, y1, x2, y2;
    cin >> x1 >> y1 >> x2 >> y2;
    
    int dx = abs(x2 - x1);
    int dy = abs(y2 - y1);
    
    if (dx == 0 || dy == 0) {
        cout << dx + dy + 1 << endl;
    } else {
        cout << gcd(dx, dy) + 1 << endl;
    }
    
    return 0;
}