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: Wrong Answer)

#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <stdlib.h>
#include <math.h>
#include <numeric>
#include <functional>
#include <stack>

int main (){
	int n;

	std::cin >> n;

	std::vector<int> v(n);

	for (size_t i = 0; i < n; i++)
	{
		std::cin >> v[i];
	}

	int count = 0;
	for (size_t i = 0; i < n - 1; i++)
	{
		if (v[i] > v[i + 1]) {
			count++;
		}
	}
	if (count > 2) {
		std::cout << "NO" << std::endl;
	}
	else {
		std::cout << "YES" << std::endl;
	}
	return 0;
}