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++14 (GCC 5.4.1) (judge verdict: Accepted)

#include <iostream>
#include <vector>
#include <queue>
#include <algorithm>

#define NMAX 2000
#define MOD 1000000007
#define INF 2000000000

#define MIN(a, b) (a < b ? a : b)
#define MAX(a, b) (a > b ? a : b)

using namespace std;

int n;
int arr[50];

bool IsSorted(int* arr, int n)
{
	for (int i = 0; i < n - 1; i++)
		if (arr[i] > arr[i + 1])
			return false;
	return true;
}

int main()
{
	cin >> n;
	for (int i = 0; i < n; i++)
		cin >> arr[i];

	if (IsSorted(arr, n))
	{
		cout << "YES\n";
		return 0;
	}
	for(int i = 0; i < n - 1; i++)
		for (int j = i + 1; j < n; j++)
		{
			swap(arr[i], arr[j]);
			if (IsSorted(arr, n))
			{
				cout << "YES\n";
				return 0;
			}
			swap(arr[i], arr[j]);
		}
	cout << "NO\n";
	return 0;
}