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: Accepted)

#include <bits/stdc++.h>

using namespace std;

int main(){
    int n;
    cin>>n;
    vector<int>a(n);
    vector<int>b(n);
    for(int i=0;i<n;i++){
        cin>>a.at(i);
        b.at(i)=a.at(i);
    }

    sort(b.begin(),b.end());

    int c=0;
    for(int i=0;i<n;i++){
        if(b.at(i)!=a.at(i)){
            c++;
        }
    }
    if(c==0){
        cout<<"YES"<<endl;
    }else if(c==2){
        cout<<"YES"<<endl;
    }else{
        cout<<"NO"<<endl;
    }
}