/* -*- coding: utf-8 -*-
 *
 * 1868.cc:  No.1868 Teleporting Cyanmond - yukicoder
 */

#include<cstdio>
#include<algorithm>
 
using namespace std;

/* constant */

const int MAX_N = 100000;

/* typedef */

/* global variables */

int rs[MAX_N], ds[MAX_N];

/* subroutines */

/* main */

int main() {
  int n;
  scanf("%d", &n);
  for (int i = 0; i < n - 1; i++) scanf("%d", rs + i);

  ds[0] = 0;
  for (int i = 0, j = 1; i < n - 1 && j < n; i++) {
    int dj = ds[i] + 1;
    while (j < rs[i]) ds[j++] = dj;
  }

  printf("%d\n", ds[n - 1]);
  return 0;
}