from bisect import bisect_right

n = int(input())
A = list(map(int, input().split()))
A = [a - i for i, a in enumerate(A)]
B = []
for a in A:
    p = bisect_right(B, a)
    if p == len(B):
        B.append(a)
    else:
        B[p] = a
print(n - len(B))