#include<iostream>

#include<cstdio>

using namespace std;

#define Min(a,b) (a<b)?a:b

const int MAX_N=;

const int INF=0x30303030;

int floors[MAX_N];

int N, A, B;

int step[MAX_N];

int dfs(int k)

{

    if(k<||k>N)    return INF;

    if(step[k]!=-)

    {

        return step[k];

    }

    if(k==B)

    {

        return ;

    }

    return step[k]=Min(dfs(k-floors[k])+,dfs(k+floors[k])+);

}

int main()

{

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

      {

          scanf("%d %d",&A, &B);

          for(int i=; i<=N; i++)

          {

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

          }

          memset(step,-,sizeof(step));

          int ans=dfs(A);

          if(ans>=INF)

          {

              printf("-1\n");

          }

          else

          {

              printf("%d\n",ans);

          }

      }

    return ;

}

#include<iostream>

#include<cstdio>

#include<cstring>

#include<queue>

using namespace std;

const int MAX_N=;

const int INF=0x30303030;

int floors[MAX_N];

int N, A, B;

typedef pair<int, int> P;

int vis[MAX_N];

int bfs()

{

    memset(vis, , sizeof(vis));

    queue<P> que;

    que.push(P(,A));

    vis[A]=;

    while(!que.empty())

    {

        P pos=que.front();que.pop();

        int k=pos.second;

        int step=pos.first;

        if(k==B)

        {

            return step;

        }

        for(int i=-; i<=; i++)

        {

            int next=(k + i*floors[k]);

            if(next>=&&next<=N&&!vis[next])

            {

                vis[next]=;

                que.push(P(step+,next));

            }

        }

    }

    return INF;

}

int main()

{

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

      {

          scanf("%d %d",&A, &B);

          for(int i=; i<=N; i++)

          {

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

          }

          int ans=bfs();

          if(ans==INF)

          {

              printf("-1\n");

          }

          else

          {

              printf("%d\n",ans);

          }

      }

    return ;

}