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)

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

int my_comp(const void *a, const void *b)
{
    return *(int*)a - *(int*)b;
}

int main(int argc, void **arg)
{
    int n;
    int p[50], q[50];
    int i, j;

    scanf("%d", &n);

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

    qsort(q, n, sizeof(int), my_comp);

    for (i = 0; i < n - 1; i++)
    {
        if( i + 1 != p[i] ) {
            for (j = i + 1; j < n; j++)
            {
                if( i + 1 == p[j] ) {
                    int t = p[i];
                    p[i] = p[j];
                    p[j] = t;
                    printf("%d %d\n", p[i], p[j]);
                    break;
                }
            }
            if( j < n ) {
                break;
            }
        }
    }

    if( memcmp(p, q, n) == 0 ) {
        printf("YES\n");
    } else {
        printf("NO\n");
    }

    return 0;
}