#include<bits/stdc++.h>
using namespace std;
int n,a,b,sum,x;
int shuzi[205];
bool shif[205];
queue<int> q;
int main()
{
	cin>>n>>a>>b;
	for(int i=1;i<=n;i++)
		cin>>shuzi[i];
	q.push(a);
	if(a==b)
	{
		cout<<0;
		return 0;
	}
	while(!q.empty())
	{
		x=q.front();
		q.pop();
		if(x==b) break;
		int e=x+shuzi[x],f=x-shuzi[x];
		if(e<=n && shif[e]==0)
		{
			sum++;
			shif[e]=1;
			q.push(e);
		}
		if(f>=1 && shif[f]==0)
		{
			sum++;
			shif[f]=1;
			q.push(f);
		}
	}
	if(x==b) printf("%d",sum);
	else printf("-1");
	return 0;
}