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(void) {
	int N;
	int count = 0;
	int k[10];
	int a, b;
	scanf("%d", &N);
	int p[50];
	for (int i = 0; i < N; i++) {
		scanf("%d", &p[i]);
		if (p[i] != i + 1) {
			k[count] = p[i];
			count++;
		}
	}
	if (count == 2) {
		a = k[0];
		b = k[1];
		if (p[a - 1] == b && p[b - 1] == a) {
			printf("YES");
		}
	}
	else if (count == 0) {
		printf("YES");
	}

	else {
		printf("NO");
	}

	return 0;

}