#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define pb push_back
const int N = 105;
int vis[2][N][N], dis[2][N][N];
int x, y, p, q;

void solve() {
	cin >> x >> y >> p >> q;
	queue<array<int, 3>>qu;
	memset(dis, 0x3f, sizeof(dis));
	dis[0][x][y] = 0;
	qu.push({0, x, y});
	while (qu.size()) {
		auto [op, a, b] = qu.front();
		qu.pop();
		if (a == 0 && op == 1) {
			cout << dis[op][a][b] << '\n';
			return ;
		}
		if (vis[op][a][b])
			continue;
		vis[op][a][b] = 1;
		if (op == 0) {
			for (int i = 0; i <= p && i <= a; i++)
				for (int j = 0; j + i <= p && j <= b; j++) {
					int ax = a - i, ay = b - j;
					int bx = x - ax, by = y - ay;
					if (ax + q >= ay || ax == 0) {
						if (dis[1][ax][ay] <= dis[op][a][b] + 1)
							continue;
						qu.push({1, ax, ay});
						dis[1][ax][ay] = dis[op][a][b] + 1;
					}
				}
		} else {
			int ax = x - a, ay = y - b;
			for (int i = 0; i <= ax && i <= p; i++)
				for (int j = 0; j <= ay && j + i <= p; j++) {
					int x1 = ax - i, y1 = ay - j;
					if (x1 + q >= y1 || x1 == 0) {
						if (dis[0][x - x1][y - y1] <= dis[op][a][b] + 1)
							continue;
						qu.push({0, x - x1, y - y1});
						dis[0][x - x1][y - y1] = dis[op][a][b] + 1;
					}
				}
		}
	}
	cout << "-1\n";
}

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