// Judges with GCC >= 12 only needs Ofast
// #pragma GCC optimize("O3,no-stack-protector,fast-math,unroll-loops,tree-vectorize")
// MLE optimization
// #pragma GCC optimize("conserve-stack")
// Old judges
// #pragma GCC target("sse4.2,popcnt,lzcnt,abm,mmx,fma,bmi,bmi2")
// New judges. Test with assert(__builtin_cpu_supports("avx2"));
// #pragma GCC target("avx2,popcnt,lzcnt,abm,bmi,bmi2,fma,tune=native")
// Atcoder
// #pragma GCC target("avx2,popcnt,lzcnt,abm,bmi,bmi2,fma")
/*
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
typedef tree<int,null_type,less<int>,rb_tree_tag,tree_order_statistics_node_update> ordered_set;
- insert(x),erase(x)
- find_by_order(k): return iterator to the k-th smallest element
- order_of_key(x): the number of elements that are strictly smaller
*/
#include<bits/stdc++.h>
using namespace std;
mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());
uniform_real_distribution<> pp(0.0,1.0);
#define int long long
#define ld long double
#define pii pair<int,int>
#define piii pair<pii,int>
#define mpp make_pair
#define fi first
#define se second
const int inf=1e18;
const int mod=998244353;
const int maxn=105;
const int bl=650;
const int maxs=655;
const int maxm=200005;
const int maxq=1000005;
const int maxl=25;
const int maxa=1000000;
const int root=3;
int power(int a,int n){
    int res=1;
    while(n){
        if(n&1) res=res*a%mod;
        a=a*a%mod;n>>=1;
    }
    return res;
}
const int iroot=power(3,mod-2);
const int base=131;

int X,Y,p,q,dp[maxn][maxn][2];
queue<piii> qq;

void f(int xt,int yt,int t){
    vector<int> x(2),y(2);
    x[t]=xt;y[t]=yt;
    x[t^1]=X-xt;y[t^1]=Y-yt;
    for(int dx=0;dx<=xt && dx<=p;dx++) for(int dy=0;dy<=yt && dx+dy<=p;dy++){
        int nx=x[t^1]+dx,ny=y[t^1]+dy;
        int px=x[t]-dx,py=y[t]-dy;
        if((px && px+q<py) || dp[nx][ny][t^1]!=-1) continue;
        dp[nx][ny][t^1]=dp[xt][yt][t]+1;
        qq.push({{nx,ny},t^1});
    }
}

void solve(){
    cin >> X >> Y >> p >> q;
    memset(dp,-1,sizeof(dp));
    dp[X][Y][0]=0;
    qq.push({{X,Y},0});
    int res=inf;
    while(!qq.empty()){
        piii cur=qq.front();qq.pop();
        if(cur.fi.fi==X && cur.se==1) res=min(res,dp[cur.fi.fi][cur.fi.se][cur.se]);
        f(cur.fi.fi,cur.fi.se,cur.se);
    }
    cout << (res==inf?-1:res) << '\n';
}

signed main(){
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);cout.tie(NULL);
    int test=1;//cin >> test;
    while(test--) solve();
}