n = int(input())
r = list(map(int, input().split()))
cur = 0
INF = 10 ** 9
ans = [INF] * n
ans[0] = 0
for i in range(n - 1):
    while cur < r[i]:
        ans[cur] = min(ans[cur], ans[i] + 1)
        cur += 1
print(ans[-1])