#include <bits/stdc++.h>
using namespace std;
int n;
int arr[100003];
double suff[100003], pref[100003], ppref[100003];
long long ft[100003][2];
void update(int a, int val, int tipe) {
  for (; a <= n; a += a & (-a)) ft[a][tipe] += val;
}
long long query(int a, int tipe) {
  long long res = 0;
  for (; a; a -= a & (-a)) res += ft[a][tipe];
  return res;
}
long long query(int a, int b, int tipe) {
  return query(b, tipe) - query(a - 1, tipe);
}
int main() {
  scanf("%d", &n);
  for (int i = 1; i <= n; i++) scanf("%d", &arr[i]);
  double div = 1.0 * n * (n + 1) / 2;
  for (int i = 1; i <= n; i++) {
    pref[i] = suff[i] = 1.0 * query(arr[i], n, 0) / div;
    update(arr[i], 1, 0);
  }
  for (int i = 1; i <= n; i++) pref[i] += pref[i - 1];
  for (int i = 1; i <= n; i++) ppref[i] = pref[i] + ppref[i - 1];
  for (int i = n; i >= 1; i--) suff[i] += suff[i + 1];
  memset(ft, 0, sizeof ft);
  double cntpref = 0, cntsuff = 0, cntmid = 0, store = 0;
  for (int i = 1; i <= n; i++) {
    store += ((i)*query(arr[i], n, 0) - query(arr[i], n, 1)) / div;
    cntsuff += suff[i + 1] * i;
    cntpref += ppref[i - 1];
    cntmid += store;
    update(arr[i], 1, 0);
    update(arr[i], i, 1);
  }
  double perm = 0;
  for (int i = 1; i <= n; i++)
    perm += 1.0 * i / div * (i - 1) * (n - i + 1) / 4.0;
  double tot = cntpref + cntsuff + cntmid + perm;
  printf("%.12lf\n", tot);
}
