#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>=&&x<=n&&!vist[x]) return true;

    return false;

}

void bfs()

{

    node cur,next;

    int i;

    cur.x=a;cur.times=;

    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=;i<;i++)

        {

            next.x=cur.x+pow(-,i)*k[cur.x];

            if(judge(next.x))

            {

                next.times=cur.times+;

                vist[next.x]=;

                q.push(next);

            }

        }

    }

    cout<<-<<endl;

}

int main()

{

    while(cin>>n,n)

    {

        int i;

        cin>>a>>b;

        for(i=;i<=n;i++) cin>>k[i];

        memset(vist,,sizeof(vist));

        vist[a]=;bfs();

    }

    return ;

}