#include <iostream>
#include <vector>
#include <map>
#include <set>
#include <algorithm>
#include <functional>
#include <queue>

using namespace std;
typedef long long i64;
int sx, sy, p, q;
struct state {
	int nx, ny; //左岸
	bool f;//船的位置
	int step;
};

bool operator==(const state&s1, const state&s2) {
	return s1.nx == s2.nx&&s1.ny == s2.ny&&s1.f == s2.f;
}
bool operator<(const state& s1, const state& s2) {
	if (s1.nx != s2.nx)return s1.nx < s2.nx;
	if (s1.ny != s2.ny)return s1.ny < s2.ny;
	if (s1.f != s2.f)return s1.f < s2.f;
	return false;
}
bool isEnd(const state&st) {
	return st.nx == 0 && st.f == 1;
}

int main() {
	ios::sync_with_stdio(false);
	cin.tie(0), cout.tie(0);
	cin >> sx >> sy >> p >> q;
	state start = {sx, sy, 0, 0}; //1->R 0->L
	bool ok = 0;
	queue<state>que;
	que.push(start);
	map<state, bool>mp;
	mp[start] = 1;
	while (!que.empty()) {
		state st = que.front();
		que.pop();
		auto[nx, ny, f, step] = st;
//		cout << nx << ' ' << ny << ' ' << f << ' ' << step << '\n';
		if (f) {
			if (isEnd(st)) {
				cout << step << '\n';
				ok = 1;
				break;
			}
		}
		if (f == 0) {
			for (int x = min(p, nx); x >= 0; x--) {
				for (int y = min(p - x, ny); y >= 0; y--) {
					//nx-x,ny-y,f
					if ((((ny - y) - (nx - x) <= q || nx == x))) {
						state st2;
						if (f == 0) {
							st2 = {nx - x, ny - y, !f, step + 1};
						} else {
							st2 = {nx + x, ny + y, !f, step + 1};
						}
						if (mp[st2]) continue;
						que.push(st2);
						mp[st2] = 1;
					}
				}
			}
		} else {
			for (int x = min(p, sx - nx); x >= 0; x--) {
				for (int y = min(p - x, sy - ny); y >= 0; y--) {
					//nx-x,ny-y,f
					if (((sy - ny - y) - (sx - nx - x) <= q || (sx - nx - x == 0))) {
						state st2;
						if (f == 0) {
							st2 = {nx - x, ny - y, !f, step + 1};
						} else {
							st2 = {nx + x, ny + y, !f, step + 1};
						}
						if (mp[st2]) continue;
						que.push(st2);
						mp[st2] = 1;
					}
				}
			}
		}
	}
	if (!ok)cout << -1 << '\n';
	return 0;
}