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<math.h>

int main() {
	int i, j, k;
	int	n, m, h, g, c, d, l, r;
	int f = 0;
	int p[55];
	int q[55];

	scanf("%d", &n);

	for (i = 0;i < n;i++) {
		scanf("%d", &p[i]);
		q[i] = p[i];
	}

	for (i = 0;i < n;i++) {
		for (j = 0;j < n-1;j++) {
			if (p[j] > p[j + 1]) {
				m = p[j];
				p[j] = p[j + 1];
				p[j + 1] = m;
			}
		}
	}

	for (i = 0;i < n;i++) {
		if (p[i] == q[i]) {
			
		}
		else {
			f = f + 1;
		}
	}

	if (f < 3) {
		printf("YES");
	}
	else {
		printf("NO");
	}



//	printf("%d", f);

	return 0;
}