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.ArrayList;
import java.util.List;
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		// TODO 自動生成されたメソッド・スタブ
		Scanner scanner = new Scanner(System.in);

//		ArrayList<Integer> p=new ArrayList<Integer>();
		int N = scanner.nextInt();
		int p[] = new int[N];
		int counter=0;

		for(int i=0;i<N;i++) {
			p[i]=scanner.nextInt();
		}

		if(p[0]-p[1]!=-1) counter++;
//		System.out.println(counter);

		for(int i=1;i<N-2;i++) {
			if(p[i]-p[i+1]!=-1) {
				counter++;
				i++;
			}
		}

		if(p[N-2]-p[N-1]!=-1) counter++;
//		System.out.println(counter);

//		System.out.println(counter);
		if(counter==0||counter==2) System.out.println("YES");
		else System.out.println("NO");

		scanner.close();


	}

}