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;
#define int long long int
#define ld long double
#define F first
#define S second
#define P pair<int,int>
#define V vector
#define pb push_back
#define mp make_pair
#define endl "\n"
#define db(...) __f(#__VA_ARGS__, __VA_ARGS__)
#define MOD 1000000007  //1e9+7

template <typename Arg1>
void __f(const char* name, Arg1&& arg1) { cout << name << " : " << arg1 << '\n'; }
template <typename Arg1, typename... Args>
void __f(const char* names, Arg1&& arg1, Args&&... args) {
    const char* comma = strchr(names + 1, ',');
    cout.write(names, comma - names) << " : " << arg1 << " | "; __f(comma + 1, args...);
}

void solve()
{
	int n; cin>>n;
	vector<int>a;
	int op1=0,op2=0,cnt=0;
	for(int i=0,x;i<n;i++){
		cin>>x;
		if(x!=i+1){
			cnt++;
			if(cnt>2){
				cout<<"NO"<<endl;
				return;
			}
			if(op1==0) op1=i+1;
			else op2=i+1;
		}
	}
	cout<<"YES"<<endl;
}
	
int32_t main()
{
    ios_base:: sync_with_stdio(false);
    cin.tie(NULL); cout.tie(NULL);
    //int t; cin>>t;
    //while(t--)
    solve();
    return 0;
}