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 main(void)
{
	int n;
	scanf("%d",&n);
	int *p;
	int *q;
	p = (int *)malloc(sizeof(int)*(n));
	q = (int *)malloc(sizeof(int)*(n));
	int i = 0;
	while (i < n)
	{
		scanf("%d",&p[i]);
		q[i] = 1+i;
		i++;
	}
	int sig = 0;
	i = 0;
	while (i < n)
	{
		if (p[i] != i+1)
			sig++;
		i++;
	}
	if (sig == 2||sig == 0)
		printf("YES\n");
	else
		printf("NO\n");
	return(0);
}