"""

"""

import sys
from sys import stdin
import heapq

N = int(stdin.readline())

R = list(map(int,stdin.readline().split()))
for i in range(N-1):
    R[i] -= 1

dp = [float("inf")] * N

q = []
dp[0] = 0
heapq.heappush( q,(0,R[0]) )

for i in range(1,N):

    while q[0][1] < i:
        heapq.heappop(q)

    dp[i] = q[0][0] + 1
    if i != N-1:
        heapq.heappush(q , (dp[i],R[i])  )

print (dp[-1])
#print (dp)