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 <cstdio>
#include <iostream>
#include <algorithm>
#include <vector>
#include <map>
#include <set>
 
using namespace std;
 
#define PB push_back
#define MP make_pairA
#define REP(i,n) for(int i=0;i<(n);i++)
bool ok(vector<int> v)
{
    REP(i,v.size())if(v[i]!=i+1)return false;
    return true;
}
int main()
{
    int n;
    cin>>n;
    vector<int>v(n);
    string ans="NO";
    REP(i,n)cin>>v[i];
    if(ok(v))ans="YES";
    for(int i=0;i<n;i++){
        for(int j=i+1;j<n;j++){
            swap(v[i],v[j]);
            if(ok(v))ans="YES";
            swap(v[i],v[j]);
        }
    }
    cout<<ans<<endl;
}