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>

template <typename InputIterator>
typename InputIterator::value_type summation(InputIterator first,
                                             InputIterator last) {
  return std::accumulate(first, last, typename InputIterator::value_type());
}
template <typename T>
std::istream &operator>>(std::istream &stream, std::vector<T> &v);
template <typename T1, typename T2>
std::istream &operator>>(std::istream &stream, std::pair<T1, T2> &p);
template <typename T>
std::istream &operator>>(std::istream &stream, std::vector<T> &v) {
  for (auto &i : v) {
    stream >> i;
  }
  return stream;
}
template <typename T1, typename T2>
std::istream &operator>>(std::istream &stream, std::pair<T1, T2> &p) {
  stream >> p.first >> p.second;
  return stream;
}

int main() {
  int64_t n;
  std::cin >> n;
  std::vector<int64_t> a(n);
  std::cin >> a;
  auto b = a;
  std::sort(b.begin(), b.end());

  int64_t p = 0;

  for (int64_t i = 0; i < n; i++) {
    if (a[i] != b[i]) {
      p++;
    }
  }
  if (p == 0 || p == 2) {
    std::cout << "YES" << std::endl;
  } else {
    std::cout << "NO" << std::endl;
  }

  return 0;
}