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++14 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include<stdio.h>
#include<iostream>
#include<iomanip>
#include<string>
#include<vector>
#include<queue>
#include<stack>
#include<map>
#include<set>
#include<algorithm>
#include<string>
#include<math.h>
using namespace std;

const int MAX = 50;

int main(){
    int N;
    int p[MAX];

    cin >> N;
    for(int i = 0;i < N;i++){
        cin >> p[i];
    }

    int cnt = 0;
    int a = 0,b = 0,c = 0,d = 0;

    for(int i = 1;i < N;i++){
        if(p[i-1] > p[i]){
            if(cnt == 0){
                a = p[i - 1];
                b = p[i];
            }
            if(cnt == 1){
                c = p[i - 1];
                d = p[i];
            }
            cnt++;
        }
    }

    if(a >= c && b >= d && cnt <= 2)cout << "YES" << endl;
    else cout << "NO" << endl;

    return 0;
}