// #pragma GCC target("avx,avx2")
// #pragma GCC optimize("Ofast")
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using uint = unsigned int;
using ull = unsigned long long;
#define rep(i,n) for(int i=0;i<int(n);i++)
#define rep1(i,n) for(int i=1;i<=int(n);i++)
#define per(i,n) for(int i=int(n)-1;i>=0;i--)
#define per1(i,n) for(int i=int(n);i>0;i--)
#define all(c) c.begin(),c.end()
#define si(x) int(x.size())
#define pb push_back
#define eb emplace_back
#define fs first
#define sc second
template<class T> using V = vector<T>;
template<class T> using VV = vector<vector<T>>;
template<class T,class U> bool chmax(T& x, U y){
	if(x<y){ x=y; return true; }
	return false;
}
template<class T,class U> bool chmin(T& x, U y){
	if(y<x){ x=y; return true; }
	return false;
}
template<class T> void mkuni(V<T>& v){sort(all(v));v.erase(unique(all(v)),v.end());}
template<class T> int lwb(const V<T>& v, const T& a){return lower_bound(all(v),a) - v.begin();}
template<class T>
V<T> Vec(size_t a) {
    return V<T>(a);
}
template<class T, class... Ts>
auto Vec(size_t a, Ts... ts) {
  return V<decltype(Vec<T>(ts...))>(a, Vec<T>(ts...));
}
template<class S,class T> ostream& operator<<(ostream& o,const pair<S,T> &p){
	return o<<"("<<p.fs<<","<<p.sc<<")";
}
template<class T> ostream& operator<<(ostream& o,const vector<T> &vc){
	o<<"{";
	for(const T& v:vc) o<<v<<",";
	o<<"}";
	return o;
}
constexpr ll TEN(int n) { return (n == 0) ? 1 : 10 * TEN(n-1); }

#ifdef LOCAL
#define show(x) cerr << "LINE" << __LINE__ << " : " << #x << " = " << (x) << endl
void dmpr(ostream& os){os<<endl;}
template<class T,class... Args>
void dmpr(ostream&os,const T&t,const Args&... args){
	os<<t<<" ~ ";
	dmpr(os,args...);
}
#define shows(...) cerr << "LINE" << __LINE__ << " : ";dmpr(cerr,##__VA_ARGS__)
#define dump(x) cerr << "LINE" << __LINE__ << " : " << #x << " = {";  \
	for(auto v: x) cerr << v << ","; cerr << "}" << endl;
#else
#define show(x) void(0)
#define dump(x) void(0)
#define shows(...) void(0)
#endif

template<class D> D divFloor(D a, D b){
	return a / b - (((a ^ b) < 0 && a % b != 0) ? 1 : 0);
}
template<class D> D divCeil(D a, D b) {
	return a / b + (((a ^ b) > 0 && a % b != 0) ? 1 : 0);
}

int d[101][101][2];	//la,lb, (left?0:1)
const int inf = 1e8;

int main(){
	cin.tie(0);
	ios::sync_with_stdio(false);		//DON'T USE scanf/printf/puts !!
	cout << fixed << setprecision(20);

	int A,B,C,D; cin >> A >> B >> C >> D;
	rep(la,A+1) rep(lb,B+1) rep(t,2) d[la][lb][t] = inf;
	using F = array<int,3>;
	queue<F> que;
	auto PUSH = [&](int la,int lb,int t,int dist){
		if(d[la][lb][t] != inf) return;
		d[la][lb][t] = dist;
		que.push(F{la,lb,t});
		if(la == 0){
			cout << dist << endl; exit(0);
		}
	};
	PUSH(A,B,0,0);
	while(!que.empty()){
		F f = que.front(); int la = f[0], lb = f[1], t = f[2];
		que.pop();
		int ra = A-la, rb = B-lb;
		if(t == 0){
			rep(da,la+1) rep(db,lb+1){
				if(da+db > C) continue;
				if(la-da > 0 && lb-db > la-da + D) continue;
				PUSH(la-da,lb-db,1,d[la][lb][t]+1);
			}
		}else{
			rep(da,ra+1) rep(db,rb+1){
				if(da+db > C) continue;
				if(ra-da > 0 && rb-db > ra-da + D) continue;
				PUSH(la+da,lb+db,0,d[la][lb][t]+1);
			}
		}
	}
	cout << -1 << endl;
}