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;
typedef long long ll;
typedef long double lb;
#define REP(i,j,n) for (int i=j;i<(n);i++)
#define RREP(i,n) for (int i = n; 0<i;i--)
#define print(out) cout<< out  << "\n";
#define mod 1000000007
const int INF = 1e9;

int main(){
  int N;cin>>N;
  vector<int> P(N);
  REP(i,0,N)cin>>P[i];
  vector<int> P_c=P;
  int pre=-1,cnt=0;
  sort(P_c.begin(),P_c.end());
  REP(i,0,N){
    if(P[i]!=P_c[i]){
      cnt++;
      if(pre==-1){
        pre=P[i];
      }
      else if(pre!=P_c[i]){
        print("NO")
        return 0;
      }
    }
  }
  print(((cnt==2)||(cnt==0)?"YES":"NO"))
  return 0;
}