#include<iostream>

#include<cstdio>

#include<cstring>

#include<algorithm>

#include<queue>

#define maxn 100005

using namespace std;

queue<int> q;

int visit[maxn],step[maxn],n,k,w[maxn],flag,t,sum;

void bfs()

{

    int head,next,i;

    while(!q.empty()) q.pop();   //注意调用前一定要清空

    q.push(n);

    visit[n]=1;

    step[n]=0;

    while(!q.empty())

    {

        head=q.front(); q.pop();//取出 并弹出队首

        for(i=1;i<=2;i++)

        {

            if(i==1) next=head-w[head];

            else  next=head+w[head];

            if(next>t||next<1) continue;//越界 

			if(!visit[next])//判重

			{

				q.push(next);

                visit[next]=1;

                step[next]=step[head]+1;

				  if(next==k) //找到终点

                  {

            	   flag=1;

            	   sum=step[next];

				   return;

                  }

			}

        }

    }

    return;

}

int main()

{

	int i;

	while(scanf("%d",&t)!=EOF&&t)

    {

    	memset(visit,0,sizeof(visit));

    //	memset(step,0,sizeof(step));//不用清空step数组 

    	scanf("%d %d",&n,&k);

    	for(i=1;i<=t;i++)

		scanf("%d",&w[i]);

		if(n==k)

		{

			printf("0\n");

			continue;

		}

		flag=0;

		bfs();

		if(flag) printf("%d\n",sum);

		else printf("-1\n");

    }

}