#include<iostream>

 #include<cstdio>

 #include<algorithm>

 #include<cstring>

 #define M 205

 #define INF 0x3f3f3f3f

 using namespace std;

 int map[M][M];

 int d[M], vis[M];

 int n;

 int b, e;

 void Dijkstra(){

    memset(d, 0x3f, sizeof(d));

    memset(vis, , sizeof(vis));

    d[b]=;

    vis[b]=;

    int root=b;

    for(int j=; j<n; ++j){

        int minLen=INF, p;

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

           if(!vis[i] && d[i] > d[root] + map[root][i])

               d[i] = d[root] + map[root][i];

           if(!vis[i] && minLen>d[i]){

              p=i;

              minLen=d[i];

           }

        }

        if(minLen==INF)

           return;

        root=p;

        vis[root]=;

    }

 }

 int main(){

    while(cin>>n && n){

        cin>>b>>e;

        memset(map, 0x3f, sizeof(map));

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

           int x, xx;

           cin>>x;

           map[i][i]=;// i+(-)x 表示 从第i层可以到达第 i+（-）x层

           xx=i-x;

           if(xx>=) map[i][xx]=;

           xx=i+x;

           if(xx<=n)  map[i][xx]=;

        }

        Dijkstra();

        if(d[e]==INF)

           cout<<"-1"<<endl;

        else

           cout<<d[e]<<endl;

    }

    return ;

 } 

 /*

 思路：当前电梯位置的两个方向进行搜索！

       注意：搜索时的界限, 用x表示将要到达的电梯的位置

             1. 首先是x>=1

             2. x<=n

             3. vis[x]!=0 表明bfs时候没有经过这个楼层

 */

 #include<iostream>

 #include<cstring>

 #include<cstdio>

 #include<queue>

 using namespace std;

 struct node{

    int x;

    int step;

    node(){}

    node(int x, int step){

       this->x=x;

       this->step=step;

    }

 };

 queue<node>q;

 int n, b, e;

 int f[];

 int vis[];

 bool bfs(){

     while(!q.empty())  q.pop();

     memset(vis, , sizeof(vis));

     q.push(node(b,));

     vis[b]=;

     while(!q.empty()){

         node cur=q.front();

         q.pop();

         if(cur.x==e){

             cout<<cur.step<<endl;

             return true;

         }

         int xx;

         xx=cur.x+f[cur.x];

         if(xx==e){

            cout<<cur.step+<<endl;

            return true;

         }

         if(xx<=n && !vis[xx]){

            q.push(node(xx, cur.step+));

            vis[xx]=;

         }

         xx=cur.x-f[cur.x];

         if(xx==e){

            cout<<cur.step+<<endl;

            return true;

         }

         if(xx>= && !vis[xx]){

            q.push(node(xx, cur.step+));

            vis[xx]=;

         }

     }

     return false;

 }

 int main(){

     while(cin>>n && n){

        cin>>b>>e;

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

           cin>>f[i];

        if(!bfs())

           cout<<"-1"<<endl;

     }

     return ;

 }