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:
    idx = bisect_right(dp,i)
    if idx: dp[idx] = i
    elif i > 0: dp[idx] = i
    #dp[bisect_right(dp,i)] = i
print(n-bisect_left(dp,INF))