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 C# (Mono 4.6.2.0) (judge verdict: Accepted)

using System;
using System.Collections.Generic;

public class CSharp{
    public static void Main(){
        Kyopuro chokudai = new Kyopuro();
	    chokudai.AtCoder();
	}
}

public class Kyopuro{

	int n;
  	int[] p;
	
    public void AtCoder(){
        string[] input;
		input = Console.ReadLine().Split(' ');
		n = int.Parse(input[0]);
      	input = Console.ReadLine().Split(' ');
      	p = new int[n];
		for (int i=0; i<n; i++) {
          p[i] = int.Parse(input[i]);
        }
      	int c = 0;
      	for (int i=1; i<=n; i++) {
          if (p[i - 1] != i) c++;
        }
      	
      	if (c == 0 || c == 2) Console.WriteLine("YES");
      	else Console.WriteLine("NO");
		
		
    }
    public static void DebugWL(object x){ System.Diagnostics.Debug.WriteLine(x); }
}