#include <bits/stdc++.h>
#define rep(i,n) for(int i = 0; i < (int)(n); i++)

using namespace std;
using LL = long long;
using P = pair<int,int>;
using vv = vector<vector<int>>;
const int INF = (int)1e9;
const LL LINF = (LL)1e18;

int main(){
	int N;
	cin >> N;
	vector<int> A(N);
	rep(i,N) cin >> A[i];
	int M = 0;
	rep(i,N) M = max(M, A[i]);
	vector<int> dp(M + 1);
	rep(i,M) dp[i+1] = i + 1;
	int ans = N;
	rep(i,N){
		int K = dp[A[i]];
		if(K == 0){
			ans--;
			continue;
		}
		rep(j,M+1){
			if(dp[j] >= K) dp[j] -= K;
		}
	}
	cout << ans << endl;

	return 0;
}