hdu A strange lift

#include"iostream"
#include"stdio.h"
#include"string.h"
#include"algorithm"
#include"cmath"
#include"queue"
#define mx 205
using namespace std;
int n,a,b;
int k[mx];
int vist[mx];
struct node
{
    int x,times;
    friend bool operator<(node t1,node t2)
    {
        return t2.times<t1.times;
    }
};
bool judge(int x)
{
    if(x>=1&&x<=n&&!vist[x]) return true;
    return false;
}
void bfs()
{
    node cur,next;
    int i;
    cur.x=a;cur.times=0;
    priority_queue<node>q;
    q.push(cur);
    while(!q.empty())
    {
        cur=q.top();
        q.pop();
        if(cur.x==b){cout<<cur.times<<endl;return;}
        for(i=0;i<2;i++)
        {
            next.x=cur.x+pow(-1,i)*k[cur.x];
            if(judge(next.x))
            {
                next.times=cur.times+1;
                vist[next.x]=1;
                q.push(next);
            }
        }
    }
    cout<<-1<<endl;
}
int main()
{
    while(cin>>n,n)
    {
        int i;
        cin>>a>>b;
        for(i=1;i<=n;i++) cin>>k[i];
        memset(vist,0,sizeof(vist));
        vist[a]=1;bfs();
    }
    return 0;
}