Problem:
Score : 200 points

Problem Statement

We have a sequence p = {p_1,\ p_2,\ ...,\ p_N} which is a permutation of {1,\ 2,\ ...,\ N}.

You can perform the following operation at most once: choose integers i and j (1 \leq i < j \leq N), and swap p_i and p_j. Note that you can also choose not to perform it.

Print YES if you can sort p in ascending order in this way, and NO otherwise.

Constraints

All values in input are integers.

2 \leq N \leq 50

p is a permutation of {1,\ 2,\ ...,\ N}.

Input

Input is given from Standard Input in the following format:

N
p_1 p_2 ... p_N

Output

Print YES if you can sort p in ascending order in the way stated in the problem statement, and NO otherwise.

Sample Input 1

5
5 2 3 4 1

Sample Output 1

YES

You can sort p in ascending order by swapping p_1 and p_5.

Sample Input 2

5
2 4 3 5 1

Sample Output 2

NO

In this case, swapping any two elements does not sort p in ascending order.

Sample Input 3

7
1 2 3 4 5 6 7

Sample Output 3

YES

p is already sorted in ascending order, so no operation is needed.

Solution in Go (1.6) (judge verdict: Accepted)

	package main

	import (
		"fmt"
		"sort"
	)

	func main()  {
		var n int
		var incorrectOrderNum int
		fmt.Scan(&n)
		nums := ScanNums(n)
		sortedNums := make([]int, n)
		copy(sortedNums, nums)
		sort.Ints(sortedNums)

		for i := 0; i < n; i++ {
			if nums[i] != sortedNums[i] {
				incorrectOrderNum++
			}
		}

		if incorrectOrderNum == 2 || incorrectOrderNum == 0 {
			fmt.Println("YES")
		} else {
			fmt.Println("NO")
		}
	}

	func ScanNums(len int) (nums []int) {
		var num int
		for i := 0; i < len; i++ {
			fmt.Scan(&num)
			nums = append(nums, num)
		}
		return
	}