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>
#define debug(x) cerr << #x << " = " << x << "\n";
#define debug_v(x) cerr << #x << " ="; for(auto in : x) {cerr << " [" << in << "]";} cerr << '\n';
using namespace std;
using ll = long long;
using ld = long double;
const double PI = acos(-1);
const int mod = 1e9 + 7;
const int inf = 1e9 + 100;
const ll inf64 = 1e18 + 100;
int main(){
	ios_base::sync_with_stdio(false);
	cin.tie(0);
	cout.tie(0);
	cout << fixed << setprecision(20);
	int n;
	cin >> n;
	vector<int> a(n);
	for (int i = 0; i < n; i++){
		cin >> a[i];
	}
	int it1 = 0, it2 = 0;
	for (int i = 0; i < n; i++){
		 if(a[i] != i + 1){
			 it1 = i;
			 break;
		 }
	}
	for (int i = it1 + 1; i < n; i++){
		if(a[i] != i + 1){
			 it2 = i;
			 break;
		 }
	}
	swap(a[it1], a[it2]);
	bool ok = true;
	for (int i = 1; i < n; i++){
		ok &= a[i] > a[i - 1];
	}
	cout << (ok ? "YES\n" : "NO\n");
	return 0;
}