#include "bits/stdc++.h"
using namespace std;
typedef long long ll;
#define INF (1<<30)
#define INFLL (1ll<<60)
typedef pair<double, int> P;
typedef pair<int, P> E;
#define MOD (1000000007ll)
#define l_ength size
#define EPS (1e-10)

void add_mod(ll &a, ll b){
	a += b;
	a %= MOD;
}

void mul_mod(ll &a, ll b){
	a *= b;
	a %= MOD;
}

int main(void){
	int n,i;
	ll a[225816],b[225816];
	fill(b,b+225816,INFLL);
	cin >> n;
	for(i=0; i<n; ++i){
		cin >> a[i];
		a[i] -= i;
	}
	for(i=0; i<n; ++i){
		*upper_bound(b,b+n,a[i]) = a[i];
	}
	cout << ((n-(int)(lower_bound(b,b+n,INFLL)-b))) << endl;
	return 0;
}