#include<bits/stdc++.h>
using namespace std;
int n,a,b,i,x[210],k[210],c,d,p,ans;
int main(){
	cin>>n>>a>>b;
	for(i=1;i<=n;i++)cin>>x[i];
	p=a;
	for(i=1;i<=n;i++){
		if(p==b){
			cout<<ans<<endl;
			return 0;
		}
		c=p+x[p];d=p-x[p];
		if(c<=n&&k[c]==0){//上楼
			p=c;
			k[c]=1;
			ans++;
		}else if(d>0&&k[d]==0){//下楼 
			p=d;
			k[d]=1;
			ans++;
		}
	}
	cout<<"-1"<<endl;
	return 0;
}