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: Runtime Error)

#include <stdio.h>
#include <stdlib.h>

int main(void){
	int p[52], N, i, count = 0, ans[3]={0};
	if(scanf("%d", &N) != 1){
		printf("scanfエラー\n");
		return 2;
	}
	for(i = 1; i <= N; i++){
		if(scanf("%d", &p[i]) != 1){
			printf("scanfエラー\n");
			return 2;
		}
		if((p[i] <= 0) || (p[i] >= 51)){
			printf("NO\n");
			return 1;
		}
	}
	for(i=1; i <= N; i++){
		p[i] -= i;
		if(p[i]!=0){
			ans[count] = abs(p[i]);
			count++;
			if(count == 3){
				printf("NO\n");
				return 1;
			}
		}
	}
	if((ans[0] == ans[1]) || (ans[0] == 0)) printf("YES\n");
	else printf("NO\n");
	return 0;
}