#include <bits/stdc++.h>
const long long mod = 1000000007ll;
using namespace std;
struct FT {
  vector<long long> s;
  FT(long long n) : s(n) {}
  void update(long long pos, long long dif) {
    for (; pos < ((long long)(s).size()); pos |= pos + 1) s[pos] += dif;
  }
  long long query(long long pos) {
    long long res = 0;
    for (; pos > 0; pos &= pos - 1) res += s[pos - 1];
    return res;
  }
  long long range(long long l, long long r) { return query(r + 1) - query(l); }
  long long lower_bound(long long sum) {
    if (sum <= 0) return -1;
    long long pos = 0;
    for (long long pw = 1 << 25; pw; pw >>= 1) {
      if (pos + pw <= ((long long)(s).size()) && s[pos + pw - 1] < sum)
        pos += pw, sum -= s[pos - 1];
    }
    return pos;
  }
};
int main() {
  cin.sync_with_stdio(0);
  long long n;
  cin >> n;
  vector<long long> perm(n);
  for (long long i = 0; i < (n); i++) {
    cin >> perm[i];
    perm[i]--;
  }
  FT ft(n);
  FT ft1s(n);
  long long invs_in_all_segs = 0;
  long long totalInvs = 0;
  for (long long i = 0; i < (n); i++) {
    invs_in_all_segs += ft.range(perm[i] + 1, n - 1) * (n - i);
    totalInvs += ft1s.range(perm[i] + 1, n - 1);
    ft.update(perm[i], i + 1);
    ft1s.update(perm[i], 1);
  }
  double totInvsAdded = 0.0;
  for (long long i = (1); i <= (n); i++) {
    totInvsAdded +=
        ((double)(i * (i - 1)) / (double)4) * ((double)(n - i + 1ll));
  }
  double avgAdded = totInvsAdded / ((double)((n * (n - 1) / 2) + n));
  double avgRem = (double)invs_in_all_segs / ((double)((n * (n - 1) / 2) + n));
  double res = (double)(totalInvs) + avgAdded - avgRem;
  cout << setprecision(15) << res << "\n";
  return 0;
}
