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>
int main(void)
{
	int n,p[51],t,i,j;
	scanf("%d", &n);
	for(i=1; i<=n; i++)
	scanf("%d", &p[i]);
	for(i=1; i<n; i++)
	{
		if(i!=p[i])
		{
			for(j=i+1; j<=n; j++)
			{
				if(i==p[j])
				{
					t=p[i];
					p[i]=p[j];
					p[j]=t;
					break;
				}
			}
			break;
		}
	}
	for(i=1; i<=n; i++)
	{
		if(i!=p[i])
		{
			printf("NO\n");
			break;
		}
		if(n==i)
		printf("YES\n");
	}
	
	return 0;
}