#include <bits/stdc++.h>
using namespace std;
const int N = 3333;
int n, m, a[N], b[N], c[N], d[N], f[N];
vector<int> v[N], h;
double ans, w[N];
int fnd(int x) {
  if (f[x] == x) return x;
  return f[x] = fnd(f[x]);
}
void dfs0(int u, int o) {
  if (b[u]) return;
  if (!b[o]) h.push_back(u);
  b[u] = 1;
  for (int i = v[u].size(); i--;) dfs0(v[u][i], o);
  if (!b[o]) h.pop_back();
}
void dfs1(int u, int fa) {
  if (b[u]) return;
  b[u] = 1;
  if (!c[u]) c[u] = c[fa];
  for (int i = v[u].size(); i--;) dfs1(v[u][i], u);
}
void dfs2(int u, int fa) {
  if (b[u]) return;
  b[u] = 1;
  d[u] = d[fa] + 1;
  for (int i = v[u].size(); i--;) dfs2(v[u][i], u);
}
int main() {
  int i, j, x, y, z;
  scanf("%d", &n);
  for (i = 1; i <= n; i = i + 1) f[i] = i, w[i] = (double)1.0 / (double)i;
  for (i = 1; i < n; i = i + 1) {
    scanf("%d%d", &x, &y);
    if (fnd(x) != fnd(y))
      v[x].push_back(y), v[y].push_back(x);
    else
      a[0] = x, a[1] = y;
  }
  memset(b, 0, sizeof(b));
  dfs0(a[1], a[0]);
  m = h.size();
  for (i = 2; i <= m; i = i + 1) a[i] = h[i - 1];
  for (i = 1; i <= m; i = i + 1) c[a[i]] = i;
  memset(b, 0, sizeof(b));
  dfs1(a[1], 0);
  for (i = 1; i <= n; i = i + 1) {
    memset(b, 0, sizeof(b));
    dfs2(i, 0);
    for (j = 1; j <= n; j = j + 1) {
      if (c[i] == c[j] && i <= j) ans += w[d[j]];
      if (c[i] >= c[j]) continue;
      x = d[j], z = x + c[i] - 1 + m - c[j], y = z - (c[j] - c[i] - 1);
      ans += w[x] + w[y] - w[z];
    }
  }
  printf("%.9lf", ans * 2);
  return 0;
}
