#include<bits/stdc++.h>
using namespace std;
struct node{
    int floor,step;
};
int n,a,t;
int k[201];
int b[201];
queue<node> q;
int main(){
    cin>>n>>a>>t;
    for (int i=1;i<=n;i++) cin>>k[i];
    int step=0;
    b[a]=1;
    q.push((node){a,0});
    while (!q.empty()){
        int floor=q.front().floor;
        int step=q.front().step;
        b[floor]=1;
        q.pop();
        if (floor==t){
            cout<<step<<endl;
            return 0;
        }
        if (floor-k[floor]>=1 and b[floor-k[floor]]==0){
            q.push((node){floor-k[floor],step+1});
        }
        if (floor+k[floor]<=n and b[floor+k[floor]]==0){
            q.push((node){floor+k[floor],step+1});
        }
    }
    cout<<-1<<endl;
    return 0;
}