/*

CodeForces 839C - Journey [ DFS,期望 ]	|	Codeforces Round #428 (Div. 2)

*/

#include <bits/stdc++.h>

using namespace std;

const int N = 100005;

int n;

vector<int> G[N];

double dp[N], val[N];

bool vis[N];

void dfs(int u, int pre)

{

    bool flag = 0;

    for (auto&v : G[u])

    {

        if (v == pre) continue;

        flag = 1;

        dp[v] = dp[u]+1;

        val[v] = val[u] / (G[u].size()-1);

        dfs(v, u);

    }

    if (!flag) vis[u] = 1;

}

int main()

{

    scanf("%d", &n);

    for (int i = 1; i < n; i++)

    {

        int u, v; scanf("%d%d", &u, &v);

        G[u].push_back(v);

        G[v].push_back(u);

    }

    G[1].push_back(1);

    val[1] = 1;

    dfs(1, 1);

    int cnt = 0;

    double ans = 0;

    for (int i = 1; i <= n; i++)

        if (vis[i]) ans += dp[i]*val[i];

    printf("%.15f\n", ans);

}