// CF_TR4_A
#define _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include <cmath>

using namespace std;

int gcd(int x, int y)
{
    if (x == 0) return y;
    else return gcd(y%x, x);
}

int main()
{
    long long x1, y1, x2, y2, k = 0, a, b;
    cin >> x1 >> y1 >> x2 >> y2;
    //scanf("%d%d%d%d", &x1, &y1, &x2, &y2);
     a = abs(x2 - x1);
     b = abs (y2 - y1);
     k = gcd (a,b);

    //cout << k;
    printf("%d", k+1);
    //system("pause");
    return 0;
}