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>
#define N 50

int insertionSort(int numbers[], int array_size)
{
  int i, j,flag=0,x=0;

  for (i=1; i < array_size; i++) { //整列されていない部分の先頭を指す
  flag=0;
    j = i; // 交換要素のためのインデックス

      // 整列済みの場合は処理しない
    while ((j > 0) && (numbers[j-1] > numbers[j])) {
      // 整列されていない隣り合う要素を交換する
      swap(&numbers[j-1], &numbers[j]);
      flag=1;
      // 隣り合う要素のインデックスを更新
      j--;
    }
    if(flag==0)x++;
  }
  return x;
}

void swap(int *p_from, int *p_to) {
    int tmp;
    tmp = *p_from;
    *p_from = *p_to;
    *p_to = tmp;
}

int main(void){
  int A[N],B=0,k,i;
  scanf("%d",&k);
  for(i=0;i<k;i++){
    scanf("%d",&A[i]);
  }
  B=insertionSort(A, k);
  if(B < 2){
    printf("YES\n");
  }else{
    printf("NO\n");
  }
  return 0;
}