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>
int main() {
  int N, i;
  int count = 0;
  scanf("%d", &N);
  int p[N];
  int q[N];
  scanf("%d", &p[0]);
  for(i = 1; i < N; ++i){
    scanf("%d", &p[i]);
    if (p[i] < p[i - 1]) {
      if (count == 0) {
        q[count] = i - 1;
      } else {
        q[count] = i;
      }
      ++count;
    }
  }
  
  if (count == 1 || count > 2) {
    printf("NO");
  }
  else if (count == 2) {
    int temp, cou;
    cou = 1;
    temp = p[q[0]];
    p[q[0]] = p[q[1]];
    p[q[1]] = temp;
    for (i = 1; i < N; ++i) {
      if (p[i] < p[i - 1]) {
        printf("NO");
        break;
      }
      ++cou;
    }
    if (cou == N) {
      printf("YES");
    }
  } else {
    printf("YES");
  }
  return 0;
}