#include <bits/stdc++.h>
#include <iostream>
 
using namespace std;
 
typedef long long ll;
typedef long double ld;
typedef unsigned long long ull;
typedef pair<int,int> PII;
typedef pair<ll,ll> PLL;
#define i128 _int128
#define fi first
#define se second 
#define pb push_back
#define endl '\n'
#define int long long
 
const ll INF=0x3f3f3f3f;
const ll N=1e2+9;
const int mod=1e4;

inline int read(){
    int ans=0,sign=1;
    char ch = getchar();
    while(ch<'0'||ch>'9'){
        if(ch=='-'){
            sign=-1;
        }
        ch=getchar();
    }
    while(ch>='0'&&ch<='9'){
        ans = ans*10 + ch-'0';
        ch = getchar();
    }
    return ans*sign;
}


int dp[N][N][2];
int x,y,p,q;
void bfs() {
    queue<pair<pair<int,int>,int>>c;
    c.push({{x,y},0});
    dp[x][y][0]=0;
    while (!c.empty()) {
        int nowx=c.front().first.first;
        int nowy=c.front().first.second;
        int flag=c.front().second;
        c.pop();
        for (int i=nowx; i>=0; i--) {
            for (int j=nowy; j>=0; j--) {
                if ((i+j<=p)&&(nowx-i+q>=nowy-j||nowx-i==0)) {
                    if (dp[x-nowx+i][y-nowy+j][flag^1]>dp[nowx][nowy][flag]+1) {
                        dp[x-nowx+i][y-nowy+j][flag^1]=dp[nowx][nowy][flag]+1;
                        c.push({{x-nowx+i,y-nowy+j},flag^1});
                    }
                    
                }
            }
        }
    }
}
void solve() {
    cin>>x>>y>>p>>q;
    for (int i=0; i<=100; i++) {
        for (int j=0; j<=100; j++) {
            for (int k=0; k<=1; k++) {
                dp[i][j][k]=1e18;
            }
        }
    }
    bfs();
    int minn=1e18;
    for (int i=0; i<=y; i++) {
        minn=min(dp[x][i][1],minn);
    }
    if (minn>=1e18) {
        cout<<"-1\n";
    } else {
        cout<<minn<<"\n";
    }
}



 
 
signed main(){
    ios::sync_with_stdio(0);cin.tie(0);cout.tie(0);
    
    int _=1;
    // fac[0]=1;
    // for(int i=1;i<=N-9;++i)fac[i]=(fac[i-1]*i)%mod;
    //_=read();
    
    while(_--)solve();
 
    return 0;
}