CF56B.Spoilt Permutation

Vasya collects coins: he has exactly one coin for every year from 1 to n. Naturally, Vasya keeps all the coins in his collection in the order in which they were released. Once Vasya's younger brother made a change — he took all the coins whose release year dated from l to r inclusively and put them in the reverse order. That is, he took a certain segment [l, r] and reversed it. At that the segment's endpoints did not coincide. For example, if n = 8, then initially Vasya's coins were kept in the order 1 2 3 4 5 6 7 8. If Vasya's younger brother chose the segment [2, 6], then after the reversal the coin order will change to 1 6 5 4 3 2 7 8. Vasya suspects that someone else could have spoilt the permutation after his brother. Help him to find that out. Check if the given permutation can be obtained from the permutation 1 2 ... n using exactly one segment reversal. If it is possible, find the segment itself.

瓦西娅收集硬币：他恰好拥有从 $1$ 到 $n$ 的每一年各一枚硬币。自然地，瓦西娅将所有硬币按其发行年份的顺序保存在自己的收藏中。某次，瓦西娅的弟弟做了一次改动——他取出了所有发行年份在 $l$ 到 $r$（含端点）之间的硬币，并将它们的顺序完全反转。也就是说，他选取了某个区间 $[l,\,r]$ 并对该区间进行翻转。此时该区间的两个端点不重合。例如，若 $n = 8$，则瓦西娅最初的硬币顺序为 1 2 3 4 5 6 7 8；若弟弟选取区间 $[2,\,6]$，则翻转后硬币顺序变为 1 6 5 4 3 2 7 8。瓦西娅怀疑，在弟弟操作之后，可能还有其他人篡改了排列。请帮助他查明此事：判断给定的排列是否能通过对初始排列 1 2 ... n 恰好执行一次区间翻转操作而得到。若可以，请找出该翻转区间。

The first line contains an integer n (1 ≤ n ≤ 1000) which is the number of coins in Vasya's collection. The second line contains space-separated n integers which are the spoilt sequence of coins. It is guaranteed that the given sequence is a permutation, i.e. it contains only integers from 1 to n, and every number is used exactly 1 time.

第一行包含一个整数 $n$（$1 \leq n \leq 1000$），表示瓦西娅收藏的硬币数量。
第二行包含 $n$ 个用空格分隔的整数，表示损坏的硬币序列。题目保证该序列是一个排列，即它仅包含从 $1$ 到 $n$ 的整数，且每个数字恰好出现一次。

If it is impossible to obtain the given permutation from the original one in exactly one action, print 0 0. Otherwise, print two numbers l r (1 ≤ l < r ≤ n) which are the endpoints of the segment that needs to be reversed to obtain from permutation 1 2 ... n the given one.

如果无法通过恰好一次操作从原始排列得到给定排列，则输出 0 0。否则，输出两个数 $l$ 和 $r$（满足 $1 ≤ l < r ≤ n$），表示需要翻转的区间端点，使得对排列 $1\ 2\ \dots\ n$ 执行该区间翻转操作后，即可得到给定排列。