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;
import java.util.Arrays;
// Arrays.toString(array) 配列arrayの中身を出力する

public class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    int N = Integer.parseInt(sc.nextLine());
    int[] p = new int[N];
    int cnt = 0;
    int temp1 = 0;
    int temp2 = 0;
    for(int i = 1; i <= N; i++){
      p[i-1] = Integer.parseInt(sc.next());
      if(p[i-1] != i){
        cnt += 1;

        if(cnt == 1){
          temp1 = i-1;
        }else if(cnt == 2){
          temp2 = i-1;
        }else{
          break;
        }

      }
    }

    if(cnt == 0){
      System.out.println("YES");
    }else if(cnt == 2){
      if(p[temp2] == temp1+1 && p[temp1] == temp2+1){
        System.out.println("YES");
      }else{
        System.out.println("NO");
      }
    }else{
      System.out.println("NO");
    }
  }
}