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;
using System.Linq;

class Program
{
    static string InputPattern = "InputX";

    static List<string> GetInputList()
    {
        var WillReturn = new List<string>();

        if (InputPattern == "Input1") {
            WillReturn.Add("5");
            WillReturn.Add("5 2 3 4 1");
            //YES
        }
        else if (InputPattern == "Input2") {
            WillReturn.Add("5");
            WillReturn.Add("2 4 3 5 1");
            //NO
        }
        else if (InputPattern == "Input3") {
            WillReturn.Add("7");
            WillReturn.Add("1 2 3 4 5 6 7");
            //YES
        }
        else {
            string wkStr;
            while ((wkStr = Console.ReadLine()) != null) WillReturn.Add(wkStr);
        }
        return WillReturn;
    }

    static void Main()
    {
        List<string> InputList = GetInputList();

        int[] PArr = InputList[1].Split(' ').Select(X => int.Parse(X)).ToArray();
        int[] SortedArr = PArr.OrderBy(X => X).ToArray();

        int DiffCnt = 0;
        for (int I = 0; I <= PArr.GetUpperBound(0); I++) {
            if (PArr[I] != SortedArr[I]) DiffCnt++;
        }
        Console.WriteLine(DiffCnt <= 2 ? "YES" : "NO");
    }
}