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: Wrong Answer)

/*
 * main.c
 *
 *  Created on: 2019/07/21
 *      Author: family
 */

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

int p[51] = {0};
int pp[2][3] = {0};
int main()
{
	int N = 0, i = 0, big1 = 0, j = 0;
	scanf("%d", &N);
	for(i = 0 ; i < N; i++) {
		scanf("%d", &p[i]);
	}
	for(i = 0 ; i < N; i++) {
		if(i != 0) {
			if(p[i-1] > p[i]) {
				big1++;
				if(j < 2) {
					pp[j][0] = p[i-1];
					pp[j][1] = p[i];
					pp[j][2] = p[i+1];
					j++;
				}
			}
		}
	}
	// ---
	if(big1 == 0) {
		printf("YES\n");
	} else if (big1 == 1){
		if (pp[0][1] == p[N-1]) {
			printf("YES\n");
		} else if (pp[0][1] < pp[0][2]){
			printf("YES\n");
		} else {
			printf("NO\n");
		}
	} else if (big1 == 2){
		if ((pp[0][0] > pp[1][0]) && (pp[0][1] > pp[1][1])) {
			if(pp[1][2] == 0) {
				printf("YES\n");
			} else {
				if(pp[0][1] < pp[1][2]) {
					printf("YES\n");
				} else {
					printf("NO\n");
				}
			}
		} else {
			printf("NO\n");
		}
	} else {
		printf("NO\n");
	}
    return 0;
}