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 <stdlib.h>
#include <stdbool.h>
#include <string.h>
#include <math.h>
#define Max(a, b) ((a) > (b) ? (a) : (b))
#define Min(a, b) ((a) > (b) ? (b) : (a))
#define Abs(x) ((x) > 0 ? (x) : -(x))
#define REP(i, n) for(int i = 0; i < n; i++)
#define INF 1000000000000 //10^12
#define MOD 1000000007 //10^9 + 7
typedef long long ll;

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

int
main(int argc, char *argv[])
{
  int n, p[100], a[100];
  scanf("%d", &n);
  REP(i, n){
    scanf("%d", &p[i]);
    a[i] = p[i];
  }

  qsort(p, n, sizeof(int), sort);
  int flag = 0;

  for(int i = 0; i < n; i++){
    if(a[i] != p[i]) flag++;
  }

  if(flag == 2 || flag == 0) printf("YES\n");
  else printf("NO\n");

  return 0;
}