#include <bits/stdc++.h>
using namespace std;
vector<vector<int> > g(100010);
vector<long double> l(100010), e(100010);
long double ans = 0;
int k = 0;
void dfs(int v, int p = -1) {
  for (int i = 0; i < g[v].size(); ++i) {
    if (g[v][i] == p) continue;
    if (v != 1) {
      e[g[v][i]] = e[v] / (g[v].size() - 1);
    } else {
      e[g[v][i]] = e[v] / g[v].size();
    }
    l[g[v][i]] = l[v] + 1;
    dfs(g[v][i], v);
  }
}
int main() {
  ios_base::sync_with_stdio(0);
  int n;
  cin >> n;
  if (n == 1) {
    cout << 0;
    return 0;
  }
  l[1] = 0;
  e[1] = 1;
  for (int i = 0; i < n - 1; i++) {
    int x, y;
    cin >> x >> y;
    g[x].push_back(y);
    g[y].push_back(x);
  }
  dfs(1);
  for (int i = 1; i <= n; i++)
    if (i != 1 && g[i].size() == 1) {
      ans += e[i] * l[i];
      k++;
    }
  cout << setprecision(10) << fixed << ans;
  return 0;
}
