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 <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <cmath>
#include <numeric>
#include <iostream>
#include <sstream>
#include <string>
#include <algorithm>
#include <vector>
#include <map>
#include <queue>
#include <stack>
#include <deque>
#include <list>
#include <unordered_map>
#include <tuple>
#include <complex>


#define FOR(i, a, b)		for(int i = (int)(a); i < (int)(b); ++i)
#define FORE(i, a, b)		for(int i = (int)(a); i <= (int)(b); ++i)
#define REP(i, n)			FOR(i, 0, n)
#define REPE(i, n)			FORE(i, 0, n)
#define ALL(x)				(x).begin(),(x).end()
#define DEBUG_DC(x)			cout << #x << ": " << x << endl
#define VEC_TYPE			int
#define INF					1e5+1

using namespace std;
typedef long long ll;
typedef vector<VEC_TYPE> vdef;
typedef vector<vdef> vvdef;
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmaxE(T& a, T b) { if (a <= b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }
template<class T> inline bool chminE(T& a, T b) { if (a >= b) { a = b; return 1; } return 0; }
template<typename T> inline T mygcd(T a, T b) { return b ? mygcd(b, a%b) : a; }
template<typename T> inline T mylcm(T a, T b) { return a * b / mygcd(a, b); }

int main()
{
	int ans = 0;
	int n;
	cin >> n;
	vdef a(n, 0);
	for (int i = 0; i < n; ++i) cin >> a[i];

	int cnt = 0;
	for (int i = 0; i < n; ++i)
	{
		if (a[i] != i + 1) ++cnt;
	}
	if (cnt <= 2)
		cout << "YES" << endl;
	else
		cout << "NO" << endl;
	//cout << ans << endl;
	return 0;
}