#coding: utf-8
#yuki365

n=int(raw_input())
a=map(int,raw_input().split())

cnt=0
i=n-1
j=n-1
while i>=0:
 if a[i]<j+1:
  cnt+=1
  i-=1
 elif a[i]>=j+1:
  i-=1
  j-=1

print cnt