#include <bits/stdc++.h>
using namespace std;
#define incID(i, l, r) for(int i = (l)    ; i <  (r); i++)
#define  inc(i, n) incID(i, 0, n)
#define  ALL(v)  v.begin(),  v.end()

// ---- ----

int n, a[200000], INF = 2e9;

int main() {
	cin >> n;
	inc(i, n) { cin >> a[i]; }
	
	vector<int> dp(n + 1, INF);
	dp[0] = 0;
	inc(i, n) {
		if(a[i] >= i) { * lower_bound(ALL(dp), a[i] - i) = a[i] - (i + 1); }
	}
	
	cout << count(ALL(dp), INF) << endl;
	
	return 0;
}