C++ :

#include <iostream>
#include <algorithm>
using namespace std;
const int N(202),oo(0x6fffffff);
int g[N][N],dist[N];
bool judge[N]={false};
int main()
{
    int n,a,b;
    cin>>n>>a>>b;
    for(int i=1;i<=n;i++)
        for(int j=1;j<=n;j++)
            if(i!=j)
                g[i][j]=oo;
    int x;
    for(int i=1;i<=n;i++)
    {
        cin>>x;
        if(i+x<=n) g[i][i+x]=1;
        if(i-x>=1) g[i][i-x]=1;
    }
    for(int i=1;i<=n;i++) dist[i]=g[a][i];
    judge[a]=true;
    for(int i=1;i<=n-1;i++)
    {
        int p,minx(oo);
        for(int t=1;t<=n;t++)
            if(minx>dist[t]&&judge[t]==false)
                minx=dist[t],p=t;
        judge[p]=true;
        for(int j=1;j<=n;j++)
            if(!judge[i])
                dist[j]=min(g[p][j]+dist[p],dist[j]);
    }
    cout<<dist[b]<<endl;
    return 0;
}