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.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.Scanner;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 *
 * @author Akash
 */
public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        B0Or1Swap solver = new B0Or1Swap();
        solver.solve(1, in, out);
        out.close();
    }

    static class B0Or1Swap {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            int n = in.nextInt();
            int a[] = new int[n];

            for (int i = 0; i < n; i++) {
                a[i] = in.nextInt();
            }
            if (check(a, n)) {
                out.println("YES");
                return;
            }

            for (int i = 0; i < n; i++) {
                for (int j = i + 1; j < n; j++) {
                    int temp = a[i];
                    a[i] = a[j];
                    a[j] = temp;
                    if (check(a, n)) {
                        out.println("YES");
                        return;
                    }
                    temp = a[i];
                    a[i] = a[j];
                    a[j] = temp;
                }
            }
            out.println("NO");
        }

        boolean check(int a[], int n) {
            for (int i = 1; i < n; i++) {
                if (a[i] < a[i - 1])
                    return false;
            }
            return true;
        }

    }
}