#include <bits/stdc++.h>

using namespace std;

#define N 1000005

int a[N];

bool visit[N];

int main(){

    int n,p,l,r;

    cin>>n>>p>>l>>r;

    for(int i=0;i<n;i++){

        cin>>a[i];

        if(a[i]<0 || a[i]>=n)

            a[i]=n;

    }

    queue<pair<int,int>> q;

    q.push({0,0});//{now,dis}

    visit[0]=1;

    int buffer;

    while(!q.empty() && q.front().first!=p){

        auto v=q.front();

        q.pop();

        buffer=v.first-l;

        if(buffer>=0 && a[buffer]!=n && visit[a[buffer]]!=1){

            q.push({a[buffer],v.second+1});

            visit[a[buffer]]=1;

        }

        buffer=v.first+r;

        if(buffer<n && a[buffer]!=n && visit[a[buffer]]!=1){

            q.push({a[buffer],v.second+1});

            visit[a[buffer]]=1;

        }

    }

    cout<<q.front().second;

    return 0;

}