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<fstream>
#include<string>
#include<vector>
#include<utility>
#include<algorithm>
#include<climits>
#include<set>
#include<map>
#include<cmath>
#include<iomanip>
#include<iterator>
#include<queue>
#include<stack>
#include<cctype>
#include<deque>

//by Skeef79

//НЕ ИСПОЛЬЗУЙ endl, есть свой en!!
//Иногда нужно не просто придумывать решение, а метматически расписать систему уравнений
//для задач с cin/cout в большом кол-ве - gnu , иначе вижуалки. А ваще пробуй два если TL

//для интерактивок - cout<<flush
// cin.tie и sync_with_stdio убирать для интерактивок

typedef long long ll;
typedef long double ld;

#define pb push_back
#define en '\n'
#define for0(i,n) for(int i = 0;i<n;i++)
#define all(x) (x).begin(),(x).end()
#define allr(x) (x).rbegin(),(x).rend()
#define vec vector
#define pii pair<int,int>
#define pll pair<ll,ll>

using namespace std;

const int INF = 1e9 + 1233;
const ll LINF = 1e18 + 1233;

template<typename T> void print(vector<T>& a)
{
	for (int i = 0; i < a.size(); i++)
		cout << a[i] << ' ';
}

template <typename T> void Input(vector<T>& a)
{
	for (int i = 0; i < a.size(); i++)
		cin >> a[i];
}

bool IsSorted(vector<int>& a)
{
	for (int i = 1; i < a.size(); i++)
	{
		if (a[i] < a[i - 1])
			return false;
	}
	return true;
}

int main()
{
	ios::sync_with_stdio(false);
	cin.tie(0);
	cout.tie(0);
	
	int n;
	cin >> n;
	vector<int> a(n);
	Input(a);

	if (IsSorted(a))
	{
		cout << "YES";
		return 0;
	}

	for (int i = 0; i < n; i++)
	{
		for (int j = i + 1; j < n; j++)
		{
			swap(a[i], a[j]);
			if (IsSorted(a))
			{
				cout << "YES";
				return 0;
			}
			swap(a[i], a[j]);
		}
	}

	cout << "NO";

}