#include<bits/stdc++.h>

using namespace std;

#define ull unsigned long long
#define ll long long
#define lowbit(x) (x)&(-x)
//#define int long long
//#define double long double 
const int N = 1e3 + 5;
const ll base = 131;
const ll mod = 998244353;
int dp[N][N][2];
struct syz{
    int a,b,c;
    syz(){}
    syz(int aa,int bb,int cc):a(aa),b(bb),c(cc)
    {}
};
void solve() {
    memset(dp,0x3f3f,sizeof(dp));
    int x,y,p,q;
    cin>>x>>y>>p>>q;
    queue<syz>Q;
    Q.push({x,y,1});
    dp[x][y][1]=0;
    while(!Q.empty()){
       auto &[u,v,z]=Q.front();
       Q.pop();
       if(z==1){
        for(int i=0;i<=u;++i){
            for(int j=0;j<=v;++j){
                int nowx=u-i,nowv=v-j;
                if(i+j>p) continue;
                if(nowx&&nowx+q<nowv) continue;
                if(dp[nowx][nowv][z^1]>dp[u][v][z]+1) dp[nowx][nowv][z^1]=dp[u][v][z]+1,Q.push({nowx,nowv,z^1});
            }
        }
       }
       else {
          for(int i=0;i<=x-u;++i){
            for(int j=0;j<=y-v;++j){
                int nowx=x-u-i,nowv=y-v-j;
                if(nowx&&nowx+q<nowv) continue;
                if(i+j>p) continue;
                nowx=u+i,nowv=v+j;
                if(dp[nowx][nowv][z^1]>dp[u][v][z]+1) dp[nowx][nowv][z^1]=dp[u][v][z]+1,Q.push({nowx,nowv,z^1});
            }
        }
       }
    }
    int mi=0x3f3f;
    for(int i=0;i<=y;++i) mi=min({mi,dp[0][i][0],dp[0][i][1]});
    if(mi>=0x3f3f) cout<<-1<<'\n';
    else cout<<mi<<'\n';
}
int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    int t = 1;
    //cin >> t;
    while (t--) solve();
}