#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int,int> ii;
#define N 105
#define eps 1e-10
#define F first
#define S second
#define INF 0x3f3f3f3f
#define mod 1000000007
int x,y,p,q,dp[N][N][2];
inline int d(int i,int j,int b){
    if(dp[i][j][b]!=-1) return dp[i][j][b];
    dp[i][j][b]=INF;
    //printf("%d,%d,%d\n",i,j,b);
    if(i<=p&&b==0){
        dp[i][j][b]=1;
        //printf("%d %d %d:%d\n",i,j,b,dp[i][j][b]);
        return 1;
    }
    for(int a=0;a<=p;++a){
        if(i-a<0) continue;
        for(int c=0;a+c<=p;++c){
            if(j-c<0||i-a>0&&j-c-(i-a)>q) continue;
            dp[i][j][b]=min(dp[i][j][b],d(x-(i-a),y-(j-c),b^1)+1);
        }
        
    }
   // printf("%d %d %d:%d\n",i,j,b,dp[i][j][b]);
    return dp[i][j][b];
}
int main(){
    int ans=1;
    scanf("%d%d%d%d",&x,&y,&p,&q);
    memset(dp,-1,sizeof(dp));
    if(d(x,y,0)==INF){
        puts("-1");
    }else{
        printf("%d\n",d(x,y,0));
    }
    return 0;
}