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

using namespace std;

int gcd(int q, int w)
{
    while (q != w)
    {
        if (q > w)
            q = q - w;
        else w = w - q;
    }
    return q;
}

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

    if ((x1 == x2) || (y1 == y2))
        k = abs(x1 - x2) + abs(y1 - y2) + 1;
    else
    if ((y1*(x2 - x1) - x1*(y2 - y1)) != 0)
        k = gcd(abs(y2 - y1), gcd(abs(-(x2 - x1)), abs(y1*(x2 - x1) - x1*(y2 - y1)))) + 1;
    else
        k = gcd(abs(y2 - y1), abs(-(x2 - x1))) + 1;

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