code839C.cpp

/*
 * Contest : Codeforces
 * Problem : 839C - Journey
 * Link    : https://codeforces.com/contest/839/problem/C
 */

#include <bits/stdc++.h>
using namespace std;

#define fastio ios::sync_with_stdio(0); cin.tie(0);

typedef long double ld;

vector<vector<int>> graph;
vector<bool> visited;

ld dfs(int no) {
  visited[no] = true;
  if (graph[no].size() == 1) return 0.;

  ld sum = 0.;
  for (auto &v : graph[no]) {
    if (!visited[v]) sum += dfs(v) + 1;
  }

  return sum / (graph[no].size() - (no != 1));
}

int main() {
  fastio

  int n; cin >> n;
  graph.resize(n + 1);
  visited.assign(n + 1, false);

  for (int i = 0; i < n - 1; ++i) {
    int a, b;
    cin >> a >> b;
    graph[a].push_back(b);
    graph[b].push_back(a);
  }

  cout << fixed << setprecision(7) << dfs(1) << '\n';

  return 0;
}