import os,sys,random,threading #sys.exit() 退出程序 #sys.setrecursionlimit(10**6) #调整栈空间 from random import randint,choice,shuffle #randint(a,b)从[a,b]范围随机选择一个数 #choice(seq)seq可以是一个列表,元组或字符串,从seq中随机选取一个元素 #shuffle(x)将一个可变的序列x中的元素打乱 from copy import deepcopy from io import BytesIO,IOBase from types import GeneratorType from functools import lru_cache,reduce #reduce(op,迭代对象) from bisect import bisect_left,bisect_right #bisect_left(x) 大于等于x的第一个下标 #bisect_right(x) 大于x的第一个下标 from collections import Counter,defaultdict,deque from itertools import accumulate,combinations,permutations #accumulate(a)用a序列生成一个累积迭代器,一般list化前面放个[0]做前缀和用 #combinations(a,k)a序列选k个 组合迭代器 #permutations(a,k)a序列选k个 排列迭代器 from heapq import heapify,heappop,heappush #heapify将列表转为堆 from typing import Generic,Iterable,Iterator,TypeVar,Union,List from string import ascii_lowercase,ascii_uppercase,digits #小写字母,大写字母,十进制数字 from math import ceil,floor,sqrt,pi,factorial,gcd,log,log10,log2,inf #ceil向上取整,floor向下取整 ,sqrt开方 ,factorial阶乘 from decimal import Decimal,getcontext #Decimal(s) 实例化Decimal对象,一般使用字符串 #getcontext().prec=100 修改精度 from sys import stdin, stdout, setrecursionlimit input = lambda: sys.stdin.readline().rstrip("\r\n") MI = lambda :map(int,input().split()) li = lambda :list(MI()) ii = lambda :int(input()) mod = int(1e9 + 7) #998244353 inf = 1<<60 py = lambda :print("YES") pn = lambda :print("NO") DIRS = [(0, 1), (1, 0), (0, -1), (-1, 0)] # 右下左上 DIRS8 = [(0, 1), (1, 1), (1, 0), (1, -1), (0, -1), (-1, -1), (-1, 0),(-1, 1)] # →↘↓↙←↖↑↗ class Interval_Edge_Graph: #左闭右开[l,r),下标从0开始 def __init__(self,N,weighted=False): self.N=N self.weighted=weighted self.graph=[[] for x in range(self.N*3)] for i in range(1,self.N): a,b=i<<1,i<<1|1 self.graph[(a-self.N)%(2*self.N)].append((i+self.N,0) if self.weighted else i+self.N) self.graph[(b-self.N)%(2*self.N)].append((i+self.N,0) if self.weighted else i+self.N) self.graph[i+2*self.N].append(((a-self.N)%(3*self.N),0) if self.weighted else (a-self.N)%(3*self.N)) self.graph[i+2*self.N].append(((b-self.N)%(3*self.N),0) if self.weighted else (b-self.N)%(3*self.N)) def Add_Edge(self,from_range,to_range,w=None): if self.weighted: assert w!=None self.graph.append([]) l,r=from_range if 0<=l<=self.N: l+=self.N else: raise IndexError("list index out of range") if 0<=r<=self.N: r+=self.N else: raise IndexError("list index out of range") while l>=1 r>>=1 l,r=to_range if 0<=l<=self.N: l+=self.N else: raise IndexError("list index out of range") if 0<=r<=self.N: r+=self.N else: raise IndexError("list index out of range") while l>=1 r>>=1 def Edges(self): edges=[] for x in range(len(self.graph)): for y in self.graph[x]: if self.weighted: y,d=y edges.append((x,y,d)) else: edges.append((x,y)) def dijkstra(g, start): dist = [inf] * len(g) dist[start] = 0 h = [(0, start)] while h: d, x = heappop(h) if d > dist[x]: continue for y, wt in g[x]: new_d = dist[x] + wt if new_d < dist[y]: dist[y] = new_d heappush(h, (new_d, y)) return dist n=ii() g=[[] for _ in range(n+1)] for u,v in enumerate(li(),1): g[u].append((v,1)) for i in range(1,n): g[i+1].append((i,0)) dij=dijkstra(g,1) print(dij[n])