#include <bits/stdc++.h>
#define syosu(x) fixed<<setprecision(x)
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int,int> P;
typedef pair<double,double> pdd;
typedef pair<ll,ll> pll;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<double> vd;
typedef vector<vd> vvd;
typedef vector<ll> vl;
typedef vector<vl> vvl;
typedef vector<string> vs;
typedef vector<P> vp;
typedef vector<vp> vvp;
typedef vector<pll> vpll;
typedef pair<int,P> pip;
typedef vector<pip> vip;
const int inf=1<<30;
const ll INF=1ll<<60;
const double pi=acos(-1);
const double eps=1e-8;
const ll mod=1e9+7;
const int dx[4]={-1,0,1,0},dy[4]={0,-1,0,1};

int n;

int main(){
	cin>>n;
	vi dp(n+2,inf);
	dp[0]=0;
	for(int i=1;i<=n;i++){
		int A;
		cin>>A;
		A-=i;
		if(A<0) continue;
		int I=upper_bound(dp.begin(),dp.end(),A)-dp.begin();
		dp[I]=A;
	}
	cout<<n+1-(lower_bound(dp.begin(),dp.end(),inf)-dp.begin())<<endl;
}