CF1165B.Polycarp Training

Polycarp wants to train before another programming competition. During the first day of his training he should solve exactly $1$ problem, during the second day — exactly $2$ problems, during the third day — exactly $3$ problems, and so on. During the $k$-th day he should solve $k$ problems.

Polycarp has a list of $n$ contests, the $i$-th contest consists of $a_i$ problems. During each day Polycarp has to choose exactly one of the contests he didn't solve yet and solve it. He solves exactly $k$ problems from this contest. Other problems are discarded from it. If there are no contests consisting of at least $k$ problems that Polycarp didn't solve yet during the $k$-th day, then Polycarp stops his training.

How many days Polycarp can train if he chooses the contests optimally?

Polycarp 希望在另一场编程竞赛前进行训练。在训练的第一天，他必须恰好解决 $1$ 道题；第二天恰好解决 $2$ 道题；第三天恰好解决 $3$ 道题；依此类推。在第 $k$ 天，他必须恰好解决 $k$ 道题。

Polycarp 有一个包含 $n$ 场比赛的列表，其中第 $i$ 场比赛包含 $a_i$ 道题。每天，Polycarp 必须从他尚未解决过的比赛中恰好选择一场，并解决其中的 $k$ 道题（第 $k$ 天）。该比赛中的其余题目将被丢弃。如果在第 $k$ 天，不存在任何尚未解决且题目数量不少于 $k$ 道的比赛，则 Polycarp 将停止训练。

如果 Polycarp 最优地选择比赛，他最多能训练多少天？

The first line of the input contains one integer $n$ ($1 \le n \le 2 \cdot 10^5$) — the number of contests.

The second line of the input contains $n$ integers $a_1, a_2, \dots, a_n$ ($1 \le a_i \le 2 \cdot 10^5$) — the number of problems in the $i$-th contest.

输入的第一行包含一个整数 $n$（$1 \le n \le 2 \cdot 10^5$）—— 表示比赛的场数。

输入的第二行包含 $n$ 个整数 $a_1, a_2, \dots, a_n$（$1 \le a_i \le 2 \cdot 10^5$）—— 表示第 $i$ 场比赛中题目的数量。

Print one integer — the maximum number of days Polycarp can train if he chooses the contests optimally.

输出一个整数——Polycarp 在最优选择比赛的情况下最多可以训练的天数。