#include<bits/stdc++.h>
using namespace std;
int s[1000005];
int main(){
    int n;
    cin >> n;
    for (int i = 1;i <= n;i ++)cin >> s[i];
    sort(s+1,s + n + 1);
    int ans = 1; 
    for (int i = 1;i <= n;i ++){
        if (s[i] > ans)continue;
        else ans ++;
    }
    cout << ans-1;
	return 0;
}