#include<bits/stdc++.h>
using namespace std;
#define pii pair<int,int>
#define ll long long
#define inf 0x3f3f3f3f
#define ull unsigned long long
#define pll pair<ll,ll>
#define ls d*2
#define rs d*2+1
#define mid (l+r)/2
#define lowbit(x) (x&(-x))
//#define endl "\n"
#define all(x) x.begin(),x.end()
//#define int long long
//mt19937 seed;
//uniform_int_distribution<int>num(0,2e9);
const int N=1e6+10;
const int M=33;



signed main(){
    ios::sync_with_stdio(false);
    cin.tie(0);cout.tie(0);
    int _=1;//cin>>_;
    while(_--){
        int x,y,p,q;
        cin>>x>>y>>p>>q;
        int dp[2][103][103];
        memset(dp,0x3f,sizeof(dp));
        dp[0][x][y]=0;
        queue<array<int,3>>s;
        s.push({0,x,y});
        while(s.size()){
            auto [id,num1,num2]=s.front();
            s.pop();
            for(int i=0;i<=min(p,id?x-num1:num1);i++){
                for(int j=0;j<=min(p,id?y-num2:num2);j++){
                    if(id==0){
                        int lshep=num1-i;
                        int rshep=x-lshep;
                        int lwolf=num2-j;
                        int rwolf=y-lwolf;
                        if((lshep+q<lwolf&&lshep)||i+j>p)continue;
                        if(dp[1][lshep][lwolf]>dp[0][num1][num2]+1)dp[1][lshep][lwolf]=dp[0][num1][num2]+1,s.push({1,lshep,lwolf});
                    }
                    else{
                        int rshep=x-num1-i;
                        int lshep=x-rshep;
                        int rwolf=y-num2-j;
                        int lwolf=y-rwolf;
                        if((rshep+q<rwolf&&rshep)||i+j>p)continue;
                        if(dp[0][lshep][lwolf]>dp[1][num1][num2]+1)dp[0][lshep][lwolf]=dp[1][num1][num2]+1,s.push({0,lshep,lwolf});
                    }
                }
            }
        }
        int ans=inf;
        for(int i=0;i<=y;i++)ans=min(ans,dp[1][0][i]);
        cout<<(ans==inf?-1:ans);
    }
}