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>
using namespace std;
#define int long long
#define pb push_back
#define endl "\n"
#define inf 1000000007
//#define for(i, a, b) for(int i=a; i<b; i++)
int dp[1000001] = {0};

void solve(){
	int n;
	cin>>n;
	int arr[n+1]={0};
	for(int i=1;i<=n;i++) cin>>arr[i];
	if(is_sorted(arr, arr+n+1)){
		cout<<"YES";
		return;
	}
	else{
		for(int i=1;i<=n;i++){
			if(arr[arr[i]]!=i){
				cout<<"NO";
				return;
			}
		}
		cout<<"YES";
	}	
}

signed main(){	
	#ifdef _DEBUG
		freopen("input.txt", "r", stdin);
    	freopen("output.txt", "w", stdout);
	#endif
	
	ios::sync_with_stdio(false);
	cin.tie(0);
	int t=1;
	//cin>>t;
	while(t--){
		solve();
	}
	return 0;
 
}