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 Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.util.*;

public class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    int N = sc.nextInt();
    int p[] = new int[N];
    boolean out = false;
    for (int i=0; i<N; i++) {
      p[i] = sc.nextInt();
    }

    out = hantei(p, N);

    if(!out){
      loop:for(int i=0; i<N-1; i++) {
        for (int j=i+1; j<N; j++) {
          int temp = 0;
          temp = p[i];
          p[i] = p[j];
          p[j] = temp;
          if(hantei(p, N)){
            out = true;
            break loop;
          } else {
            temp = p[j];
            p[j] = p[i];
            p[i] = temp;
          }
        }
      }
    }

    if(out){
      System.out.println("YES");
    } else {
      System.out.println("NO");
    }
  }

  public static boolean hantei(int p[], int N){
    boolean out = false;
    for (int i=0; i<N-1; i++) {
      if(p[i] > p[i+1]){
        break;
      }
      if(i == N-2){
        out = true;
      }
    }
    return out;
  }
}