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 Kotlin (1.0.0) (judge verdict: Accepted)

import java.util.*

fun main(vararg args: String) {
    val scanner = Scanner(System.`in`)
    val n = scanner.nextInt()
    val arr = IntArray(n)
    repeat(n) {
        arr[it] = scanner.nextInt()
    }
    // 1 7 4 5 6 2 9
    val indexes = LinkedList<Int>()
    var p = 0
    for (i in 0 until n) {
        val a = arr[i]
        if (a < p) {
            if (indexes.isEmpty()) {
                indexes.add(i - 1)
            } else {
                indexes.add(i)
            }
        }
        p = a
    }
    if (indexes.isEmpty()) {
        println("YES")
        return
    }
    if (indexes.size != 2) {
        println("NO")
        return
    }
    val left = arr[indexes[0]]
    val leftSmaller = arr.getOrElse(indexes[0] - 1) { 0 }
    val leftBigger = arr.getOrElse(indexes[0] + 1) { 51 }
    val right = arr[indexes[1]]
    val rightSmaller = arr.getOrElse(indexes[1] - 1) { 0 }
    val rightBigger = arr.getOrElse(indexes[1] + 1) { 51 }
    if (right in leftSmaller..leftBigger && left in rightSmaller..rightBigger) {
        println("YES")
    } else {
//        println("NO, $right !in $leftSmaller..$leftBigger nor $left !in $rightSmaller..$rightBigger")
        println("NO")
    }
}