import sys
input = sys.stdin.readline
from collections import *

N = int(input())
R = list(map(int, input().split()))
G = [[] for _ in range(N)]

for i in range(N-1):
    G[i].append((R[i]-1, 1))
    
for i in range(1, N):
    G[i].append((i-1, 0))

q = deque([0])
dist = [-1]*N
dist[0] = 0

while q:
    v = q.popleft()
    
    for nv, w in G[v]:
        if dist[nv]!=-1:
            continue
        
        dist[nv] = dist[v]+w
        
        if w==0:
            q.appendleft(nv)
        else:
            q.append(nv)

print(dist[-1])