#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
using pii = pair<int, int>;
using ppi = pair<pii, int>;
using vi = vector<int>;
int N = 5e5 + 10;
vector<ld> B1, B2;
void add(vector<ld>& B, int i, int x) {
  int n = B.size();
  for (; i < n; i += i & (-i)) B[i] = B[i] + x;
}
ld sum(vector<ld>& B, int i) {
  ld sum = 0;
  for (; i > 0; i -= i & (-i)) sum = sum + B[i];
  return sum;
}
void solve() {
  int n;
  cin >> n;
  B1.assign(n + 5, 0);
  B2.assign(n + 5, 0);
  vector<int> arr(n);
  for (int& e : arr) cin >> e;
  ll sum1 = 0, sum2 = 0;
  ld fin = 0;
  ld tot = (1LL * n * (n + 1)) / 2;
  for (int i = n - 1; i >= 0; i--) {
    int c = arr[i];
    sum1 += sum(B1, c);
    sum2 += sum(B2, c);
    fin += sum2;
    add(B1, c, 1);
    add(B2, c, n - i);
  }
  ld ans = sum1 - fin / tot + (tot - 1) / 12;
  cout << fixed << setprecision(30) << ans << endl;
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  int t = 1;
  while (t--) solve();
}
