import bisect
import copy
import decimal
import fractions
import heapq
import itertools
import math
import random
import sys
import time
from collections import Counter,deque,defaultdict
from functools import lru_cache,reduce
from heapq import heappush,heappop,heapify,heappushpop,_heappop_max,_heapify_max
def _heappush_max(heap,item):
    heap.append(item)
    heapq._siftdown_max(heap, 0, len(heap)-1)
def _heappushpop_max(heap, item):
    if heap and item < heap[0]:
        item, heap[0] = heap[0], item
        heapq._siftup_max(heap, 0)
    return item
from math import gcd as GCD
read=sys.stdin.read
readline=sys.stdin.readline
readlines=sys.stdin.readlines

def LIS(lst,weakly=False,inf=float('inf'),restoration=False):
    f=bisect.bisect_right if weakly else bisect.bisect_left
    N=len(lst)
    update=[None]*N
    dp=[inf]*N
    for k,x in enumerate(lst):
        i=f(dp,x)
        dp[i]=x
        update[k]=(i,dp[i])
    len_lis=bisect.bisect_left(dp,inf)
    if restoration:
        lis=[None]*len_lis
        len_lis-=1
        for i,x in update[::-1]:
            if i==len_lis:
                lis[len_lis]=x
                len_lis-=1
        return lis
    else:
        return len_lis

N=int(readline())
A=list(map(int,readline().split()))
for i in range(N):
    A[i]-=i
ans=N-LIS(A,weakly=True)
print(ans)