#define _USE_MATH_DEFINES

#include <bits/stdc++.h>
using namespace std;
using i32 = int; using i64 = long long int; using f64 = double; using str = string;
template <typename T> using vec = vector<T>;
template <typename T> using heap = priority_queue<T, vec<T>, greater<T>>;
#define times(n, i) for (i32 i = 0; i < (n); ++i)
#define range(a, b, i) for (i32 i = (a); i < (b); ++i)
#define upto(a, b, i) for (i32 i = (a); i <= (b); ++i)
#define downto(a, b, i) for (i32 i = (a); i >= (b); --i)
#define all(xs) (xs).begin(), (xs).end()
#define sortall(xs) sort(all(xs))
#define reverseall(xs) reverse(all(xs))
#define uniqueall(xs) (xs).erase(unique(all(xs)), (xs).end())
#define even(x) (((x) & 1) == 0)
#define odd(x) (((x) & 1) == 1)
#define append emplace_back
#define findge lower_bound
#define findgt upper_bound
const i64 MOD = 1000000007;
const f64 EPS = 1e-10;

template <typename T> T gcd(T a, T b) { while (b != 0) { swap(a, b); b = b%a; } return abs(a); }

i64 a, b, c, d;

i32 main()
{
    cin >> a >> b >> c >> d;
    if (a > c) {
        swap(a, c);
    }
    if (b > d) {
        swap(b, d);
    }
    if (a == c || b == d) {
        cout << 0 << endl;
        return 0;
    }
    i64 ans = gcd(a - c, d - b) - 1;
    ans += (c - a - 1) + (d - b - 1) + 1 - ans*2;
    cout << ans << endl;
    return 0;
}