#yuki1868
INF=float('inf')
n=int(input())
r=list(map(int,input().split()))
x=0
res=[INF]*n
res[0]=0
for i in range(n-1):
 while x<r[i]:
  res[x]=min(res[x],res[i]+1)
  x+=1
print(res[-1])