//#pragma GCC optimize("Ofast,no-stack-protector")
//#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx")
//#pragma GCC optimize("Ofast,fast-math")
//#pragma GCC target("avx,avx2")
//#pragma GCC optimize(2)
//#pragma GCC optimize(3)
//#pragma GCC optimize("Ofast")
#include <bits/stdc++.h>
using namespace std;
//#define int long long
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef double db;
#define F(i, a, b) for(int i = a; i <= (b); ++i)
#define F2(i, a, b) for(int i = a; i < (b); ++i)
#define dF(i, a, b) for(int i = a; i >= (b); --i)
template<typename T> void debug(string s, T x) {
	cerr << "[" << s << "] = [" << x << "]\n";
}
template<typename T, typename... Args> void debug(string s, T x, Args... args) {
	for (int i = 0, b = 0; i < (int)s.size(); i++) if (s[i] == '(' || s[i] == '{') b++;
	else if (s[i] == ')' || s[i] == '}') b--;
	else if (s[i] == ',' && b == 0) {
		cerr << "[" << s.substr(0, i) << "] = [" << x << "] | ";
		debug(s.substr(s.find_first_not_of(' ', i + 1)), args...);
		break;
	}
}
#ifdef ONLINE_JUDGE
#define Debug(...)
#else
#define Debug(...) debug(#__VA_ARGS__, __VA_ARGS__)
#endif
#define pb push_back
#define fi first
#define se second
#define Mry fprintf(stderr, "%.3lf MB\n", (&Med - &Mbe) / 1048576.0)
#define Try cerr << 1e3 * clock() / CLOCKS_PER_SEC << " ms\n";
typedef long long ll;
// namespace Fread {const int SIZE = 1 << 17; char buf[SIZE], *S, *T; inline char getchar() {if (S == T) {T = (S = buf) + fread(buf, 1, SIZE, stdin); if (S == T) return '\n';} return *S++;}}
// namespace Fwrite {const int SIZE = 1 << 17; char buf[SIZE], *S = buf, *T = buf + SIZE; inline void flush() {fwrite(buf, 1, S - buf, stdout), S = buf;} inline void putchar(char c) {*S++ = c;if (S == T) flush();} struct NTR {~NTR() {flush();}} ztr;}
// #ifdef ONLINE_JUDGE
// #define getchar Fread::getchar
// #define putchar Fwrite::putchar
// #endif
inline int ri() {
	int x = 0;
	bool t = 0;
	char c = getchar();
	while (c < '0' || c > '9') t |= c == '-', c = getchar();
	while (c >= '0' && c <= '9') x = (x << 3) + (x << 1) + (c ^ 48), c = getchar();
	return t ? -x : x;
}
inline void wi(int x) {
	if (x < 0) {
		putchar('-'), x = -x;
	}
	if (x > 9) wi(x / 10);
	putchar(x % 10 + 48);
}
inline void wi(int x, char s) {
	wi(x), putchar(s);
}
bool Mbe;
// mt19937 rnd(chrono::steady_clock::now().time_since_epoch().count());
const int mod = 998244353;
const int inf = 0x3f3f3f3f;
const ll infll = 0x3f3f3f3f3f3f3f3f;
const int _ = 2e5 + 5;

int f[105][105][2], x, y, P, q;

bool Med;
signed main() {
	// Mry;
	x = ri(), y = ri(), P = ri(), q = ri();
	memset(f, 0x3f, sizeof f);
	f[x][y][0] = 0;
	int ans = inf;
	auto work = [&]() -> void {
		F(t, 1, 100) {
			dF(i, x, 0) dF(j, y, 0) F(p, 0, 1) if(f[i][j][p] != inf) {
	//			Debug(t, i, j, p, f[i][j][p]);
				if(p == 0) { // 在左侧
					F(yx, 0, i) F(yy, 0, min(j, P - yx)) if(yx + yy <= P){ // 运多少
						int shengx = i - yx, shengy = j - yy;
	//					int youx = x - shengx, youy = y - shengy;
	//					Debug("11", yx, yy, i,j,shengx, shengy);
						if(shengx + q >= shengy || !shengx) {
	//						Debug(shengx, shengy);
							f[shengx][shengy][1] = min(f[shengx][shengy][1], f[i][j][p] + 1);
						}
					}
				} else {
					if(!i) {
						ans = min(ans, f[i][j][p]);
						Debug(t, i, j, p);
						return;
					}
					int youx = x - i, youy = y - j;
					F(yx, 0, youx) F(yy, 0, min(youy, P - yx)) if(yx + yy <= P){
						int zoux = x - (youx - yx), zouy = y - (youy - yy);
						if((youx - yx) + q >= (youy-yy) || !(youx-yx)) {
							f[zoux][zouy][0] = min(f[zoux][zouy][0], f[i][j][p] + 1);
						}
					}
				}
			}
		}
	};
	work();
	F(i, 0, 3) F(j, 0, 3) F(p, 0, 1) {
		Debug(i, j, p, f[i][j][p]);
	}
	Debug(f[2][3][1]);
	cout << (ans == inf ? -1 : ans) <<'\n';
	// Try;
	return 0;
}