#include <bits/stdc++.h>
using namespace std;
using ull=unsigned long long;
using ll=long long;
struct node{
    int x,y,len;
};
int x,y,p,q;
bool flag[110][110];
bool check(int x1,int y1,int x2,int y2){
    int yun_1=p-(x1-x2);
    if(yun_1<0) return false;
    if(y1-yun_1>x2+q&&x2)   return false;
    int yun_2=y2-(y1-yun_1);
    if(yun_2<0||yun_2>p)    return false;
    if(x-x2+q<y-y2&&x-x2&&x2) return false;
    return true;
}
int main() {
    ios::sync_with_stdio(0),cin.tie(0);
    int _ = 1;
    cin>>x>>y>>p>>q;
    queue<node> qe;
    qe.push({x,y,0});
    while(!qe.empty()){
        node z=qe.front();qe.pop();
        if(z.x==0){
            cout<<z.len-1<<'\n';
            return 0;
        }
        for(int i=max(0,z.x-p);i<=z.x;i++){
            for(int j=max(0,z.y-p);j<=y;j++){
                if(z.x==i&&z.y==j)  continue;
                if(!flag[i][j]&&check(z.x,z.y,i,j)){
                    qe.push({i,j,z.len+2});
                    flag[i][j]=1;
                }
            }
        }
    }
    cout<<-1<<'\n';
    return 0;
}