C++ :

#include<iostream>
#include<cstdio>
#include<cstdlib>
#include<cmath>
#include<cstring>
using namespace std;
int x[300],n,m,k,d[5000][5000],e,i,j,kk;
int main()
{
 //freopen("lift.in","r",stdin);
 //freopen("lift.out","w",stdout);
 cin>>n>>m>>kk;
 for (i=1;i<=n;++i)
  for (j=1;j<=n;++j)
   d[i][j]=5000;
 for (i=1;i<=n;++i)
 {
  cin>>x[i];
  if (i-x[i]>=1) d[i][i-x[i]]=1;
  if (i+x[i]<=n) d[i][i+x[i]]=1;
 }
 for (k=1;k<=n;++k)
  for (i=1;i<=n;++i)
    for (j=1;j<=n;++j)
     if (d[i][k]+d[k][j]<d[i][j]&&d[i][k]>0&&d[k][j]>0)
      d[i][j]=d[i][k]+d[k][j];
 /*for (i=1;i<=n;++i)
  for (j=1;j<=n;++j)
   cout<<d[i][j]<<" ";*/
 if (m==kk) cout<<"0";
 else
  if (d[m][kk]<5000) cout<<d[m][kk];
   else cout<<"-1";
 //fclose(stdin);
 //fclose(stdout);
 return 0;
}