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>
const int mod=1e9+7;
using LL=long long;
using namespace std;
namespace ndifix{

}//end of namespace ndifix

int main(){
  int n;cin>>n;
  vector<int> p(n);for(int i=0;i<n;i++)cin>>p[i];

  bool flag=1;
  for(int i=0;i<n-1;i++)if(p[i]>p[i+1])flag=0;
  if(flag){cout<<"YES"<<endl;return 0;}
  for(int i=0;i<n;i++){
  for(int j=i+1;j<n;j++){
    flag=1;
    vector<int> a=p;
    swap(a[i],a[j]);
    for(int i=0;i<n-1;i++)if(a[i]>a[i+1])flag=0;
    if(flag){cout<<"YES"<<endl;return 0;}
  }}

  cout<<"NO"<<endl;
  return 0;
}