#include<bits/stdc++.h>
using namespace std;
#define int long long
const int N = 1e5 + 5;
// a[32];
using PII = pair<int, int>;
const int INF = 0x3f3f3f3f3f3f;
map<string, vector<PII>>mp;
map<int, string>mpp;
int a[N];
int ans[N];
int ww[N];
int st[N],top=0;
const int mod = 998244353;
bool cmp(PII a, PII b) {
	return a.first > b.first;
}
bool cmp2(int a, int b) {
	return a > b;
}
int __gcd(int x, int y) {
	if (y == 0)return x;
	else return __gcd(y, x % y);
}
int fp(int a, int x) {
	int ans = 1;
	while (x) {
		if (x & 1)ans *= a;
		ans %= mod;
		a *= a;
		a %= mod;
		x >>= 1;
	}
	return ans%mod;
}

vector<int>p[N];
void solve() {
	int x, y, p, q;
	cin >> x >> y >> p >> q;
	int x2=0, y2 = 0;
	int nx=0, ny = 0;
	if (p >= x) {
		cout << 1 << endl;
		return;
	}
	int ans = 0;
	int cnt = 0;
	while (x) {
		//cnt++;
		//cout << cnt << endl;
		//cout << x << " " << y << endl;
		bool flag = 0;
		if (x == nx && y == ny) {
			cout << -1 << endl;
			return;
		}
		else if(flag)
		nx = x, ny = y;
		if (x + q < y - p) {
			cout << -1 << endl;
			return;
		}
		int s = y - (x + q);
		y -= max(s, 0LL);
		if (x <= p) {
			ans++;
			break;
		}
		for (int i = p-max(0LL,s); i >= 0; i--) {
			if (x - i + q >= y- (p - max(0LL, s)-i)) {
				x -= i;
				if (x + q < y) {
					int pp = y - (x + q);
					y-=pp;
					y2 += pp;
				}
				else if (i == 0) {
						y -= q;
						y2 += q;
				
				}
				x2 += i;
				ans++;
				flag = 1;
				break;
			}
			
		}
		y2 += max(s,0LL);
		int t = y2 - (x2 + q);
		if (x2 == 0)t = 0;
		if (t > p) {
			cout << -1 << endl;
			break;
		}
		if (x2 + q < y2 - p) {
			cout << -1 << endl;
			return;
		}
		ans++;
		y2 -= max(t, 0LL);
		y += max(t, 0LL);
		
	}
	cout << ans << endl;
}



signed main() {
	ios::sync_with_stdio(0);
	cin.tie(0), cout.tie(0);
	int t=1;
	//cin >> t;
	while (t--)solve();
}