#pragma GCC target("avx2")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#include <bits/stdc++.h>
using namespace std;

int main(){
  int N;
  cin>>N;
  vector<int> S(N-1),A(N,1e9);
  A[0] = 0;
  for(int i=0;i<N-1;i++){
    cin>>S[i];
    S[i]--;
    for(int j=i+1;j<=S[i];j++) A[j] = min(A[j],A[i]+1);
  }
  cout<<A[N-1]<<endl;
}