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 (GCC 5.4.1) (judge verdict: Accepted)

#include<stdio.h>
#include<stdlib.h>
int cmp(const void *a,const void *b)
{
	return *(int *)a - *(int *)b;
}
int main(void)
{
	int n;
	int a[100];
	int b[100];
	scanf("%d",&n);
	int i;
	int count = 0;
	int flag = 1;
	for(i=1;i<=n;i++)
	{
		scanf("%d",&a[i]);
		b[i] = a[i];
	}
	qsort(b+1,n,sizeof(b[1]),cmp);
	for(int i = 1;i<=n;i++)
	{
	//	prin
		if(a[i] != b[i])
			count++;
	}
	if(count <= 2)
		printf("YES");
	else printf("NO");
	return 0;
}