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 is_syouzyunn(const int* data, int size) {
	int i;
	for (i = 1; i < size; i++) {
		if (data[i - 1] > data[i]) return 0;
	}
	return 1;
}

int main(void) {
	int N;
	int p[64];
	int i, j;
	if (scanf("%d", &N) != 1) return 1;
	for (i = 0; i < N; i++) {
		if (scanf("%d", &p[i]) != 1) return 1;
	}
	if (is_syouzyunn(p, N)) {
		puts("YES");
		return 0;
	}
	for (i = 0; i < N; i++) {
		for (j = i + 1; j < N; j++) {
			int t;
			t = p[i]; p[i] = p[j]; p[j] = t;
			if (is_syouzyunn(p, N)) {
				puts("YES");
				return 0;
			}
			t = p[i]; p[i] = p[j]; p[j] = t;
		}
	}
	puts("NO");
	return 0;
}