from collections import deque

n = int(input())
r = list(map(int,input().split()))

tansaku = [0] * n
dp = [0] * n

mada = deque([0])
tmp = 0

while mada:
	i = mada.popleft()
	if i < n-1:
		for j in range(max(tmp, i+1), r[i]):
			if tansaku[j] == 0:
				tansaku[j] = 1
				mada.append(j)
				dp[j] = dp[i] + 1
		tmp = max(tmp, r[i])

print(dp[n-1])