CF388A.Fox and Box Accumulation

Fox Ciel has n boxes in her room. They have the same size and weight, but they might have different strength. The i-th box can hold at most x__i boxes on its top (we'll call x__i the strength of the box).

Since all the boxes have the same size, Ciel cannot put more than one box directly on the top of some box. For example, imagine Ciel has three boxes: the first has strength 2, the second has strength 1 and the third has strength 1. She cannot put the second and the third box simultaneously directly on the top of the first one. But she can put the second box directly on the top of the first one, and then the third box directly on the top of the second one. We will call such a construction of boxes a pile.

Fox Ciel wants to construct piles from all the boxes. Each pile will contain some boxes from top to bottom, and there cannot be more than x__i boxes on the top of i-th box. What is the minimal number of piles she needs to construct?

狐狸雪莉的房间里有 $n$ 个箱子。它们大小和重量均相同，但强度可能不同。第 $i$ 个箱子最多能承受 $x_i$ 个箱子叠在其上方（我们将 $x_i$ 称为该箱子的强度）。

由于所有箱子大小相同，雪莉无法将多个箱子同时直接叠放在某个箱子的正上方。例如，假设雪莉有三个箱子：第一个箱子强度为 $2$，第二个为 $1$，第三个也为 $1$。她不能将第二个和第三个箱子同时直接叠放在第一个箱子的上方。但她可以将第二个箱子直接叠放在第一个箱子上方，再将第三个箱子直接叠放在第二个箱子上方。我们将这种箱子堆叠结构称为“堆”（pile）。

狐狸雪莉希望用全部箱子构造若干堆。每堆从上到下包含若干箱子，且对任意第 $i$ 个箱子，其正上方的箱子总数不能超过 $x_i$。她至少需要构造多少堆？

The first line contains an integer n (1 ≤ n ≤ 100). The next line contains n integers _x_1, _x_2, ..., x__n (0 ≤ x__i ≤ 100).

第一行包含一个整数 $n$（$1 \leq n \leq 100$）。下一行包含 $n$ 个整数 $x_1,\ x_2,\ \dots,\ x_n$（$0 \leq x_i \leq 100$）。

Output a single integer — the minimal possible number of piles.

输出一个整数——堆的最小可能数量。

In example 1, one optimal way is to build 2 piles: the first pile contains boxes 1 and 3 (from top to bottom), the second pile contains only box 2.

In example 2, we can build only 1 pile that contains boxes 1, 2, 3, 4, 5 (from top to bottom).

在示例 1 中，一种最优方案是构建 2 堆：第一堆自上而下包含箱子 1 和 3，第二堆仅包含箱子 2。

在示例 2 中，我们只能构建 1 堆，该堆自上而下包含箱子 1、2、3、4、5。