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 <bits/stdc++.h>
using namespace std;
#define rep(i, n) for(int i = 0; i < (int)(n); i++)
#define all(x) (x).begin(),(x).end()
typedef long long ll;
const int INF = 1000000000;
const long INF64 = 1000000000000000ll;
const int MOD = 1000000007;
int main(){
	int n;
	bool han=false;
	std::cin >> n;
	std::vector<int> a(n);
	rep(i,n)std::cin >> a[i];
	rep(i,n)rep(j,n){{
		std::vector<int> b(n);
		int counter=0;
		rep(k,n)b[k]=a[k];
		rep(k,n-1)if(b[k]>b[k+1])counter++;
		if(counter==0)han=true;
		
		if(i!=j){
			swap(b[i],b[j]);
			counter=0;
			//rep(k,n)std::cout << b[k];
			rep(k,n-1)if(b[k]>b[k+1])counter++;
			if(counter==0)han=true;
		}
	}}
	if(han)std::cout << "YES" << std::endl;
	else std::cout << "NO" << std::endl;
}