//Author: Kevin
#include<bits/stdc++.h>
//#pragma GCC optimize("O2")
using namespace std;
#define ll long long
#define ull unsigned ll
#define pb emplace_back
#define mp make_pair
#define ALL(x) (x).begin(),(x).end()
#define rALL(x) (x).rbegin(),(x).rend()
#define srt(x) sort(ALL(x))
#define rev(x) reverse(ALL(x))
#define rsrt(x) sort(rALL(x))
#define sz(x) (int)(x.size())
#define inf 0x3f3f3f3f
#define pii pair<int,int>
#define lb(v,x) (int)(lower_bound(ALL(v),x)-v.begin())
#define ub(v,x) (int)(upper_bound(ALL(v),x)-v.begin())
#define uni(v) v.resize(unique(ALL(v))-v.begin())
#define longer __int128_t
void die(string S){puts(S.c_str());exit(0);}
int dp[110][110][2];
int n,m,p,q;
int main()
{
	ios_base::sync_with_stdio(false);
	cin.tie(0);
	cout.tie(0);
	cin>>n>>m>>p>>q;
	memset(dp,-1,sizeof(dp));
	queue<int> qu;
	for(int i=0;i<=m;i++)
	{
		dp[0][i][1]=0;
		qu.push(0);
		qu.push(i);
		qu.push(1);
	}
	while(!qu.empty())
	{
		int a=qu.front();qu.pop();
		int b=qu.front();qu.pop();
		int c=qu.front();qu.pop();
		if(c==1)
		{
			for(int x=0;x<=n-a;x++)
				for(int y=0;y<=p-x&&y<=m-b;y++)
					if(n-a-x==0||n-a-x+q>=m-b-y)
						if(dp[a+x][b+y][0]==-1)
						{
							dp[a+x][b+y][0]=dp[a][b][1]+1;
							qu.push(a+x);
							qu.push(b+y);
							qu.push(0);
						}
		}
		else
		{
			for(int x=0;x<=a;x++)
				for(int y=0;y<=p-x&&y<=b;y++)
					if(a==x||a-x+q>=b-y)
						if(dp[a-x][b-y][1]==-1)
						{
							dp[a-x][b-y][1]=dp[a][b][0]+1;
							qu.push(a-x);
							qu.push(b-y);
							qu.push(1);
						}
		}
	}
	cout<<dp[n][m][0]<<endl;
	return 0;
}