from collections import deque

N = int(input())
R = list(map(int, input().split()))
seen = [False]*N
dis = [0]*N
posi = 0
d = deque()
d.append(0)
while d:
    v = d.popleft()
    if v == N-1:
        break
    for i in range(max(posi, v+1), R[v]):
        if not seen[i]:
            dis[i] = dis[v]+1
            seen[i] = True
            d.append(i)
    posi = max(posi, R[v])
print(dis[-1])