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.*;
public class Main {
	Scanner sc = new Scanner(System.in);
	int a,b,c,d,e,f,k,l,m,n,x,y,z;
	int[] p1;
	int[] p2;
	int ans;
	String[] S;

	Main(){
		// 整数の入力
		n = sc.nextInt();
		p1 = new int[n];
		p2 = new int[n];

		for(int i=0;i<n;i++){
			p1[i]=sc.nextInt();
			p2[i]=p1[i];
		}

		Arrays.sort(p2);

		for(int i=0;i<n;i++){
			ans += p1[i]==p2[i]?0:1;
		}

		// 出力
		System.out.println(ans>2?"NO":"YES");
	}

	public static void main(String[] args){
		new Main();
	}
}