#ifndef LOCAL
#pragma GCC optimize ("Ofast")
#pragma GCC optimize ("unroll-loops")
#endif

#include <bits/stdc++.h>
using namespace std;

using ll=long long;
using uint=unsigned;

#define rng(i,a,b) for(int i=int(a);i<int(b);i++)
#define rep(i,b) rng(i,0,b)
#define pb push_back
#define eb emplace_back
#define all(x) x.begin(),x.end()
#define si(x) int(x.size())
#define a first
#define b second
#define fr first
#define sc second
#define mp make_pair
template<class t>using vc=vector<t>;

template<class t,class u> bool chmax(t&a,u b){if(a<b){a=b; return true;}else return false;}
template<class t,class u> bool chmin(t&a,u b){if(a>b){a=b; return true;}else return false;}

template<class t,class u>
ostream& operator<<(ostream&os,const pair<t,u>&p){
	return os<<"{"<<p.a<<","<<p.b<<"}";
}
template<class t>ostream& operator<<(ostream&os,const vector<t>&v){
	os<<"{";
	for(auto e:v)os<<e<<",";
	return os<<"}";
}

using P=pair<int,int>;

int x,y,p,q;
int dp[2][102][102];
bool used[2][102][102];

void solve(){
	cin>>x>>y>>p>>q;
	
	rep(i,2)rep(j,102)rep(k,102){
		dp[i][j][k]=-1;
		used[i][j][k]=false;
	}
	queue<pair<int,pair<int,int>>> que;
	dp[0][x][y]=0;
	que.push(mp(0,mp(x,y)));
	while(!que.empty()){
		auto r=que.front(); que.pop();
		if(used[r.fr][r.sc.fr][r.sc.sc])continue;
		used[r.fr][r.sc.fr][r.sc.sc]=true;
		if(r.fr==0){
			for(int i=0;i<=p;i++){
				for(int j=0;i+j<=p;j++){
					if(r.sc.fr<i)continue;
					if(r.sc.sc<j)continue;
					if(r.sc.fr-i+q<r.sc.sc-j)continue;
					if(dp[1][r.sc.fr-i][r.sc.sc-j]==-1){
						dp[1][r.sc.fr-i][r.sc.sc-j]=dp[0][r.sc.fr][r.sc.sc]+1;
						que.push(mp(1,mp(r.sc.fr-i,r.sc.sc-j)));
					}
				}
			}
		}
		else {
			for(int i=0;i<=p;i++){
				for(int j=0;i+j<=p;j++){
					if(x-r.sc.fr<i)continue;
					if(y-r.sc.sc<j)continue;
					if(x-r.sc.fr-i+q<y-r.sc.sc-j)continue;
					if(dp[0][r.sc.fr+i][r.sc.sc+j]==-1){
						dp[0][r.sc.fr+i][r.sc.sc+j]=dp[1][r.sc.fr][r.sc.sc]+1;
						que.push(mp(0,mp(r.sc.fr+i,r.sc.sc+j)));
					}
				}
			}
		}
	}
	rep(i,2)rep(j,x+1)rep(k,y+1){
		cerr<<i<<" "<<j<<" "<<k<<" "<<dp[i][j][k]<<endl;
	}
	cout<<dp[1][0][0]<<endl;
}

signed main(){
	cin.tie(0);
	ios::sync_with_stdio(0);
	cout<<fixed<<setprecision(20);
	solve();
}

/*
4 4 3 1
0 0 0 6
0 0 1 6
0 0 2 6
0 0 3 6
0 0 4 6
0 1 0 6
0 1 1 4
0 1 2 4
0 1 3 4
0 1 4 4
0 2 0 -1
0 2 1 4
0 2 2 4
0 2 3 2
0 2 4 2
0 3 0 -1
0 3 1 -1
0 3 2 2
0 3 3 2
0 3 4 2
0 4 0 -1
0 4 1 -1
0 4 2 -1
0 4 3 2
0 4 4 0
1 0 0 5
1 0 1 5
1 0 2 -1
1 0 3 -1
1 0 4 -1
1 1 0 5
1 1 1 3
1 1 2 3
1 1 3 -1
1 1 4 -1
1 2 0 3
1 2 1 3
1 2 2 3
1 2 3 1
1 2 4 -1
1 3 0 3
1 3 1 3
1 3 2 1
1 3 3 1
1 3 4 1
1 4 0 3
1 4 1 1
1 4 2 1
1 4 3 1
1 4 4 1
5
*/

/*
3 5 2 0
0 0 0 -1
0 0 1 -1
0 0 2 -1
0 0 3 -1
0 0 4 -1
0 0 5 -1
0 1 0 -1
0 1 1 -1
0 1 2 -1
0 1 3 -1
0 1 4 -1
0 1 5 -1
0 2 0 -1
0 2 1 -1
0 2 2 -1
0 2 3 -1
0 2 4 -1
0 2 5 -1
0 3 0 -1
0 3 1 -1
0 3 2 -1
0 3 3 -1
0 3 4 -1
0 3 5 0
1 0 0 -1
1 0 1 -1
1 0 2 -1
1 0 3 -1
1 0 4 -1
1 0 5 -1
1 1 0 -1
1 1 1 -1
1 1 2 -1
1 1 3 -1
1 1 4 -1
1 1 5 -1
1 2 0 -1
1 2 1 -1
1 2 2 -1
1 2 3 -1
1 2 4 -1
1 2 5 -1
1 3 0 -1
1 3 1 -1
1 3 2 -1
1 3 3 1
1 3 4 -1
1 3 5 -1
-1
*/