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 <string> 
#include <vector> 
#include <algorithm> 
#include <utility> 
#include <tuple> 
#include <cstdint> 
#include <cstdio> 
#include <map> 
#include <queue> 
#include <set> 
#include <stack> 
#include <deque> 
#include <unordered_map> 
#include <unordered_set> 
#include <bitset> 
#include <cctype> 
#include<math.h>
using namespace std;
//#define int long long
#define m_p make_pair
#define mod 1000000007
#define rep(i,n)  for(int i=0; i<(int) (n); i++)
#define all(v)  v.begin(),v.end()
#define vecin(v) for(int i=0; i<(int)v.size(); i++)cin>>vec[i];
using namespace std;

int jousu(int, int);
int jousu(int x00, int y00) {
	int z00 = 1;
	for (int i = 0; i < y00; i++) {
		z00 *= x00;
	}
	return z00;
}
int kurai(int x00, int y00) {
	int z00 = (x00 % jousu(10, y00)) / jousu(10, y00 - 1);
	return z00;
}
int keta(int x00) {
	int z00 = x00;
	int w00 = 0;
	while (z00 != 0) {
		z00 /= 10;
		w00++;
	}
	return w00;
}



int main() {
	int n,cou=0;
	cin >> n;
	vector<int>vec(n),vec2(n);
	vecin(vec);
	vec2 = vec;
	sort(all(vec));
	rep(i, n) {
		if (vec[i] != vec2[i])cou++;
	}
	if (cou <= 2) {
		cout << "YES" << endl;
	}
	else {
		cout << "NO" << endl;
	}
}