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#include <bits/stdc++.h>
using namespace std;
const int N = 1e6 + 10;//题单数量上限
int a[N];//每套题单里面的题的数量
int main() {
int n;
cin >> n;
for (int i = 1; i <= n; i++)
cin >> a[i];
sort(a + 1, a + 1 + n);
int h = 1;//排完序后，待比较的题单号
for (int i = 1;;) { //枚举每一天，依赖break停止
if (a[h] >= i) //允许，可以走到一天
i++;
if (++h > n) {
cout << i - 1 << endl;
break;
}
return 0;
