P4379 [USACO18OPEN] Lemonade Line S

 

#include<cstdio>
#include<cstring>
#include<iostream>
#include<algorithm>
#include<bits/stdc++.h>
#define ll long long
#define ddd printf("-----------------debug\n");
using namespace std;

int a[100010],n,sum=0;
int main()
{
    ios::sync_with_stdio(false);cin.tie(0);
    cin>>n;
    for(int i=1;i<=n;i++) cin>>a[i];
    sort(a+1,a+1+n); 
    for(int i=n;i>=1;i--)
    {
        if(a[i]>=sum) sum++;
    }
    cout<<sum<<'\n';
    return 0;
}