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];
    	P[0] = sc.nextInt();
    	int error = 0;
    	boolean asc = true;
    	boolean once = true;
    	for (int i = 1; i < N; i++) {
    		P[i] = sc.nextInt();
    		if (once && !asc && error - 1 == P[i - 1]) {
    			asc = true;
				once = false;
    		} else if (P[i] < P[i - 1]) {
    			error = P[i - 1];
    			asc = false;
    		}
    	}
    	System.out.println(asc ? "YES" : "NO");
    }
}