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 Java8 (OpenJDK 1.8.0) (judge verdict: Wrong Answer)

import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = Integer.parseInt(sc.next());
		int[] a = new int[n];
		for (int i = 0; i < n; i++) {
			a[i] = Integer.parseInt(sc.next());
		}
		String ans = canBeAscending(n, a) ? "YES" : "NO";
		System.out.println(ans);
	}

	static boolean canBeAscending(int n, int[] a) {
		int count = 0;
		for (int i = 0; i < n - 1; i++) {
			if (a[i] != i + 1) {
				for (int j = i + 1; j < n; j++) {
					if (a[j] != j + 1) {
						if (count >= 1) {
							return false;
						}
						swap(a, i, j);
						count++;
						break;
					}
				}
			}
		}
		return true;
	}

	static void swap(int[] a, int n1, int n2) {
		int tmp = a[n1];
		a[n1] = a[n2];
		a[n2] = tmp;
	}
}