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 <bits/stdc++.h>
#include <cstdio>
using namespace std;
typedef long long int ll; // Long long

#define vi vector<int>
#define vii vector<vector<int> >
#define vi_(n) vector<int>((n))
#define vii_(n,m) vector<vector<int> >((n), vector<int>((m)))
#define vi_def(n, def) vector<int>((n), (def))
#define vii_def(n, m, def) vector<vector<int> >((n), vector<int>((m), (def)))

#define rep(i, n) for(int i=0; i < (n); ++i)
#define per(i, n) for(int i=(n)-1 i >= 0; --i)

int main(){
	int N;
	cin >> N;
	vi p(N);
	rep(i, N){
		int P;
		cin >> P;
		p[i] = P;
	}

	int cnt = 0;
	rep(i, N){
		if(p[i] != i){
			++cnt;
		}
	}

	cout << (cnt >= 3 ? "NO" : "YES") << endl;

}