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.Linq;

namespace abc135_b
{
    static class Program
    {
        static void Main(string[] args)
        {
            var n = Console.ReadLine().ToInteger();
            var p = Console.ReadLine().ToIntArray();

            var order = p.OrderBy(m => m).ToArray();

            var count = 0;
            for (int i = 0; i < p.Length; i++)
            {
                if (p[i] != order[i])
                {
                    count++;
                    if (count > 3)
                    {
                        break;
                    }
                }
            }

            Console.WriteLine($"{(count <= 2 ? "YES" : "NO")}");
        }

        static int ToInteger(this string s)
        {
            return int.Parse(s);
        }

        static int[] ToIntArray(this string s, char separator = ' ')
        {
            return s.Split(separator).Select(m => m.ToInteger()).ToArray();
        }
    }
}