#include <bits/stdc++.h>
using namespace std;
#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) (v).begin(),(v).end()
#define fi first
#define se second
template<typename A, typename B> inline bool chmax(A &a, B b) { if (a<b) { a=b; return 1; } return 0; }
template<typename A, typename B> inline bool chmin(A &a, B b) { if (a>b) { a=b; return 1; } return 0; }
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<int, pii> pip;
const ll INF = 1ll<<29;
const ll MOD = 1000000007;
const double EPS  = 1e-10;
const bool debug = 0;
//----------------------//

ll gcd(ll a, ll b) {
	if (b == 0) return a;
	return gcd(b, a % b);
}

int main() {
	ll a, b, c, d;
	cin >> a >> b >> c >> d;
	
	ll x = abs(a - c), y = abs(b - d);
	
	ll ans;
	if (x == 0) {
		ans = y;
	} else {
		ans = y + x - 1;
		ans -= x / (x / gcd(x, y)) - 1;
	}
	
	cout << ans << endl;
	
	return 0;
}
