#include<bits/stdc++.h>
using namespace std;
inline int read() {
	int x = 0, f = 1;
	char ch = getchar();
	while(ch < '0' || ch > '9') {
		if(ch == '-') f = -1;
		ch = getchar();
	}
	while(ch >= '0' && ch <= '9') {
		x = (x << 1) + (x << 3) + (ch ^ 48);
		ch = getchar();
	}
	return x * f;
} 
int x, y, p, q;
bool vis[110][110][110];
int ans = 10000;

struct Node {
	int a, b, c, t;
};
void solve() {
	queue<Node> s;
	s.push({x, y, 0, 0});
	while(!s.empty()) {
		Node tmp = s.front();
		s.pop();
		int a = tmp.a, b = tmp.b, c = tmp.c, t = tmp.t;
		if(a < 0 || b < 0 || t > 100 || a > x || b > y) continue;
		if(vis[a][b][t]) continue;
		vis[a][b][t] = 1;
		//cout << a << " " << b << " " << c << " " << t << endl;
		if(c == 0) {
			if(a <= p) {
				cout << t + 1;
				return;
			}
			for(int i = 0; i <= p; ++i) { //i羊 
				for(int j = 0; j <= p - i; ++j) {
					if(a - i + q < b - j) continue;
					s.push({a - i, b - j, 1, t + 1});
				}
			}
		}
		else {
			//cout << p << endl;
			for(int i = 0; i <= p; ++i) { //i羊 
				for(int j = 0; j <= p - i; ++j) {
					if(x - a - i + q < y - b - j && x - a - i >= 1) continue;
					s.push({a + i, b + j, 0, t + 1});
				}
			}
		}
	}
	cout << -1;
	return;
} 
int main() {
	x = read();
	y = read();
	p = read();
	q = read();
	solve();
}