#include <bits/stdc++.h>
using namespace std;

#define lp(i, a, b) for (int i = (int)(a); i < (int)(b); i++)
#define rep(i, n) lp(i, 0, n)
#define rlp(i, a, b) for (int i = (int)(b) - 1; i >= (int)(a); i--)
#define rrep(i, n) rlp(i, 0, n)

#define mp make_pair
#define mt make_tuple
#define pb push_back
#define eb emplace_back
#define all(c) begin(c), end(c)

typedef long long ll;
typedef unsigned long long ull;

const int dx[] = {-1, 0, 1, 0, -1, -1, 1, 1};
const int dy[] = {0, -1, 0, 1, -1, 1, -1, 1};

const int MOD = 1e9 + 7;
const int INF = 1 << 28;
const ll INFLL = 1ll << 60;

template<typename T>
inline void unique(T &c){
	sort(all(c));
	c.erase(unique(all(c)), end(c));
}

ll x, y, a, b;

ll dot(ll x, ll y, ll a, ll b)
{
	return x * a + y * b;
}

ll cross(ll x, ll y, ll a, ll b)
{
	return x * b - y * a;
}

int main()
{
	cin >> x >> y >> a >> b;
	ll res = max(abs(x), abs(y));
	if (dot(x, y, a, b) > 0 && cross(x, y, a, b) == 0){
		res++;
	}
	cout << res << endl;
}