#include <iostream> 
#include <algorithm> 
#include <cstring> 
#include <cstdio>
#include <vector> 
#include <queue> 
#include <cstdlib> 
#include <iomanip>
#include <cmath> 
#include <ctime> 
#include <map> 
#include <set> 
using namespace std; 
#define lowbit(x) (x&(-x)) 
#define max(x,y) (x>y?x:y) 
#define min(x,y) (x<y?x:y) 
#define MAX 100000000000000000 
#define MOD 1000000007
#define pi acos(-1.0) 
#define ei exp(1) 
#define PI 3.141592653589793238462
#define ios() ios::sync_with_stdio(false)
#define INF 0x3f3f3f3f 
#define mem(a) (memset(a,0,sizeof(a))) 
typedef long long ll;
int dis[250],g[250][250],vis[250];
int a[250],n,x,y,k;
void init()
{
    for(int i=1;i<=n;i++)
    {
        for(int j=1;j<i;j++)
        {
            g[i][j]=g[j][i]=INF;
        }
        g[i][i]=0;
    }
}
void dij(int x)
{
    for(int i=1;i<=n;i++)
    {
        dis[i]=g[x][i];
        vis[i]=0;
    }
    vis[x]=1;
    int minn,v=x;
    for(int i=1;i<n;i++)
    {
        minn=INF;
        for(int j=1;j<=n;j++)
        {
            if(!vis[j] && minn>dis[j])
            {
                minn=dis[j];
                v=j;
            }
        }
        if(minn==INF) break;
        vis[v]=1;
        for(int j=1;j<=n;j++)
        {
            if(!vis[j]) dis[j]=min(dis[j],dis[v]+g[v][j]);
        }
    }
}
int main()
{
    while(scanf("%d",&n)&&n)
    {
        init();
        scanf("%d%d",&x,&y);
        for(int i=1;i<=n;i++)
        {
            scanf("%d",&k);
            if(i-k>=1) g[i][i-k]=1;
            if(i+k<=n) g[i][i+k]=1;
        }
        dij(x);
        printf("%d\n",dis[y]==INF?-1:dis[y]);
    }
    return 0;
}

#include <iostream> 
#include <algorithm> 
#include <cstring> 
#include <cstdio>
#include <vector> 
#include <queue> 
#include <cstdlib> 
#include <iomanip>
#include <cmath> 
#include <ctime> 
#include <map> 
#include <set> 
using namespace std; 
#define lowbit(x) (x&(-x)) 
#define max(x,y) (x>y?x:y) 
#define min(x,y) (x<y?x:y) 
#define MAX 100000000000000000 
#define MOD 1000000007
#define pi acos(-1.0) 
#define ei exp(1) 
#define PI 3.141592653589793238462
#define ios() ios::sync_with_stdio(false)
#define INF 0x3f3f3f3f 
#define mem(a) (memset(a,0,sizeof(a))) 
typedef long long ll;
int vis[250],x,n;
int dis[250],y,xx;
struct node
{
    int x;
    int step;
}ans,pos;
int bfs(int A,int B)
{
    queue<node>q;
    memset(vis,0,sizeof(vis));
    vis[A]=1;
    pos.x=A;pos.step=0;
    q.push(pos);
    while(!q.empty())
    {
        pos=q.front();
        q.pop();
        if(pos.x==B) return pos.step;
        xx=pos.x+dis[pos.x];
        if(x<=n && !vis[xx])
        {
            ans.x=xx;
            ans.step=pos.step+1;
            vis[xx]=1;
            q.push(ans);
        }
        xx=pos.x-dis[pos.x];
        if(x>=1 && !vis[xx])
        {
            ans.x=xx;
            ans.step=pos.step+1;
            vis[xx]=1;
            q.push(ans);
        }
    }
    return -1;
}
int main()
{
    while(scanf("%d",&n)&&n)
    {
        scanf("%d%d",&x,&y);
        for(int i=1;i<=n;i++)
        {
            scanf("%d",&dis[i]);
        }
        printf("%d\n",bfs(x,y));
    }
    return 0;
}