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.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class Main{
	public static void main(String[] args) {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		String line;
		int n = 0;
		try {
			line = br.readLine();
			n = Integer.parseInt(line);
		} catch (IOException e) {
			e.getStackTrace();
		}
		int p[] = new int [n];
		String in[] = new String [n];
		try {
			line = br.readLine();
			in = line.split(" ");
		} catch (IOException e) {
			e.getStackTrace();
		}
		int count = 0;
		for(int i = 0; i < n; i++) {
			p[i] =  Integer.parseInt(in[i]);
			if(p[i] != i+1) count++;
		}
		
		if(count <= 2) {
			System.out.println("YES");
		} else {
			System.out.println("NO");
		}
	}
}