#include <bits/stdc++.h>
using namespace std;
long long n;
long long N[100006];
long long sum[1000006], S[1000006];
long long t[1000006];
long long t1[1000006];
long long lowbit(long long u) { return u & (-u); }
void add(long long u, long long w) {
  while (u <= n) {
    t[u] += w;
    u += lowbit(u);
  }
}
long long Find(long long u) {
  long long ans = 0;
  while (u) {
    ans += t[u];
    u -= lowbit(u);
  }
  return ans;
}
void add1(long long u, long long w) {
  while (u <= n) {
    t1[u] += w;
    u += lowbit(u);
  }
}
long long Find1(long long u) {
  long long ans = 0;
  while (u) {
    ans += t1[u];
    u -= lowbit(u);
  }
  return ans;
}
double ans;
signed main() {
  scanf("%lld", &n);
  for (long long i = 1; i <= n; i++) scanf("%lld", &N[i]);
  for (long long i = 1; i <= n; i++) {
    sum[i] += Find(n) - Find(N[i]);
    S[i] += Find1(n) - Find1(N[i]);
    if (sum[i] != 0)
      ans += ((double)(n * (n + 1ll) / 2ll) * sum[i] -
              (double)(n - i + 1ll) * S[i]) /
             (double)(n * (n + 1ll) / 2ll);
    add(N[i], 1);
    add1(N[i], i);
  }
  for (long long i = 2; i <= n; i++)
    ans += (double)((i - 1) * i) / 2.00 / 2.00 * (double)(n - i + 1) /
           (double)(n * (n + 1ll) / 2ll);
  printf("%.12lf\n", ans);
  return 0;
}
