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 Java (OpenJDK 11.0.6) (judge verdict: Accepted)

import java.util.*;

public class Main {
	public static void main(String[] args) {
		Main main = new Main();
		main.run();
	}

	public void run() {
		Scanner sc = new Scanner(System.in);
		int n=sc.nextInt();
		int p[] =new int[n];


		int cnt=0;
		for(int i=0; i<n; i++) {
			p[i]=sc.nextInt();
			if(i>0 && p[i-1]>p[i]) {
				cnt++;
			}
		}
		if(cnt==0) {
			System.out.println("YES");
			sc.close();
			return;
		}
		for(int i=0; i<n; i++) {
			for(int j=i+1; j<n; j++) {
				int tmp = p[j];
				p[j] = p[i];
				p[i] = tmp;
				cnt=0;
				for(int k=0; k<n; k++) {
					if(k>0 && p[k-1]>p[k]) {
						cnt++;
					}
				}
				if(cnt==0) {
					System.out.println("YES");
					sc.close();
					return;
				}
				tmp = p[j];
				p[j] = p[i];
				p[i] = tmp;
			}
		}
		System.out.println("NO");
		sc.close();
	}
}