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: Accepted)

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[] p = new int[N];
		int idx;
		int wrongCnt = 0;
		int wrongIdx1 = 0;
		int wrongIdx2 = 0;
		for (idx = 0; idx < N; idx++) {
			p[idx] = Integer.parseInt(sc.next());
			if (p[idx] != (idx + 1)) {
				++wrongCnt;
				if (wrongCnt == 1) {
					wrongIdx1 = idx;
				} else if (wrongCnt == 2) {
					wrongIdx2 = idx;
				} else {
					break;
				}
			}
		}

		boolean flag = false;
		if (wrongCnt == 0) {
			flag = true;
		} else if (wrongCnt == 2) {
			if ((wrongIdx1 + 1) == p[wrongIdx2] && (wrongIdx2 + 1) == p[wrongIdx1]) {
				flag = true;
			}
		}

		if (flag) {
			System.out.println("YES");
		} else {
			System.out.println("NO");
		}

	}

}