#!/usr/bin/ python3.8
import sys
read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines

N, *A = map(int, read().split())


def longest_increasing_subsequence(seq, wider_sense=True):
    from bisect import bisect_left, bisect_right
    f = bisect_right if wider_sense else bisect_left
    N = len(seq)
    INF = 10**18
    dp = [INF] * (N + 1)
    for x in seq:
        if x <= 0:
            continue
        i = f(dp, x)
        dp[i] = x
    return f(dp, INF - 1)


B = [x - i for i, x in enumerate(A)]
answer = N - longest_increasing_subsequence(B)
print(answer)