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: Wrong Answer)

import java.util.Arrays;
import java.util.Scanner;

/**
 * B - 0 or 1 Swap
 */
public class Main {

    public static void main(String[] args) {

        Scanner sc = new Scanner( System.in );
        // 最大値
        int n = sc.nextInt();
        int[] p = new int[n];
        int[] q = new int[n];
        int replaceCnt = 0;
        String result = "YES";

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

//        String beforeStr = Arrays.toString( p );
//        System.out.println( "beforeStr : " + beforeStr);
        Arrays.sort( q );
//        String sortStr = Arrays.toString( p );
//        System.out.println( "sortStr : " + sortStr);
        for( int i = 0; i < n; i++ ) {
//            System.out.println( "beforeStr - " + beforeStr.charAt( i ) + ": sortStr - " + sortStr.charAt( i ) + ": replaceCnt - " + replaceCnt);
            if( p[i] != q[i] ) {
//                System.out.println( "replaceCnt++" );
                replaceCnt++;
//                System.out.println( "beforeStr - " + beforeStr.charAt( i ) + ": sortStr - " + sortStr.charAt( i ) + ": replaceCnt - " + replaceCnt);
                if( replaceCnt > 3 ) {
                    result = "NO";
                    break;
                }
            }
        }

        System.out.println( result );

        sc.close();
    }
}