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.*;

class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int[] p = new int[n];
		String result = "YES";
		int count = 0;
		int tmp1 = 0;
		int tmp2 = 0;
		for (int i = 0; i < n; i++) {
			p[i] = sc.nextInt();
		}
		for (int i = 0; i < n; i++) {
			if (p[i] != i + 1) {
				count++;
				if (count == 1) {
					tmp1 = i;
				}
				if (count == 2) {
					tmp2 = i;
				}
			}
		}
		if (count > 2) {
			result = "NO";
		}
		if (count == 2) {
			int tmp = p[tmp1];
			p[tmp1] = p[tmp2];
			p[tmp2] = tmp;
		}
		for (int i = 0; i < n; i++) {
			if (p[i] != i + 1) {
				result = "NO";
			}
		}
		System.out.println(result);
	}
}