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.Scanner;

public class Main {

  public static void main(String[] args) {

    Scanner sc = new Scanner(System.in);

    int n = sc.nextInt();
    int[] p = new int[n];
    boolean ok = true;

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

    for (int i = 0; i < n; i++) {
      if (p[i] != (i + 1)) {
        if (ok) {
          int index = 0;
          for (int j = i + 1; j < n; j++) {
            if (p[j] == (i + 1)) {
              index = j;
              break;
            }
          }
          int tmp = p[i];
          p[i] = p[index];
          p[index] = tmp;
          ok = false;
        } else {
          System.out.println("NO");
          return;
        }
      }
    }

    System.out.println("YES");

  }
}