#include <bits/stdc++.h>
using namespace std;
#pragma GCC optimize("Ofast")
int ah = 911382323;
int bh = 972663749;
template <typename F, typename S>
ostream &operator<<(ostream &os, const pair<F, S> &p) {
  return os << "(" << p.first << ", " << p.second << ")";
}
template <typename T>
ostream &operator<<(ostream &os, const vector<T> &v) {
  os << "{";
  typename vector<T>::const_iterator it;
  for (it = v.begin(); it != v.end(); it++) {
    if (it != v.begin()) os << ", ";
    os << *it;
  }
  return os << "}";
}
template <typename T>
ostream &operator<<(ostream &os, const set<T> &v) {
  os << "[";
  typename set<T>::const_iterator it;
  for (it = v.begin(); it != v.end(); it++) {
    if (it != v.begin()) os << ", ";
    os << *it;
  }
  return os << "]";
}
template <typename F, typename S>
ostream &operator<<(ostream &os, const map<F, S> &v) {
  os << "[";
  typename map<F, S>::const_iterator it;
  for (it = v.begin(); it != v.end(); it++) {
    if (it != v.begin()) os << ", ";
    os << it->first << " = " << it->second;
  }
  return os << "]";
}
long long dx[8] = {1, -1, 0, 0, 1, 1, -1, -1};
long long dy[8] = {0, 0, 1, -1, 1, -1, 1, -1};
vector<long double> ep;
void dfs(long long u, vector<long long> adj[], long long p = -1) {
  long double sum = 0;
  long long cnt = 0;
  for (auto x : adj[u]) {
    if (x != p) {
      dfs(x, adj, u);
      sum += (ep[x]);
      cnt++;
    }
  }
  if (cnt) {
    ep[u] = sum / cnt + 1;
  }
}
int32_t main() {
  ios::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  long long n;
  cin >> n;
  vector<long long> adj[n];
  ep.resize(n);
  for (long long i = (long long)1; i < (long long)n; i++) {
    long long u, v;
    cin >> u >> v;
    u--, v--;
    adj[u].emplace_back(v);
    adj[v].emplace_back(u);
  }
  dfs(0, adj);
  cout << fixed << setprecision(12) << ep[0];
}
