n = int(input())
*a, = map(int,input().split())
for i in range(n): a[i] -= i
from bisect import bisect_left, bisect_right
INF = 1<<60
dp = [INF]*n
for i in a:
    if i>0: dp[bisect_right(dp,i)] = i
print(n-bisect_left(dp,INF))