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 = sc.nextInt();
		
		int[] map = new int[N];
		for (int i = 0; i < N; i++) {
			map[i] = sc.nextInt();
		}
		
		if (check(map)) {
			System.out.println("YES");
			return;
		}
		
		for (int i = 0; i < map.length-1; i++) {
			for (int j = i+1; j < map.length; j++) {
				
				int tmp = map[i];
				map[i] = map[j];
				map[j] = tmp;
				
				if (check(map)) {
					System.out.println("YES");
					return;
				}
				
				map[j] = map[i];
				map[i] = tmp;
				
			}
		}
	
		System.out.println("NO");
	}
	
	static boolean check(int[] map) {
		int pre = 0;
		for (int i : map) {
			if (pre > i) {
				return false;
			}
			pre = i;
		}
		return true;
	}
	
}