#include<bits/stdc++.h>

using namespace std;

#define MAXN 100010

int tot , n;

int head[MAXN];

bool visited[MAXN];

double f[MAXN];

struct edge

{

        int to , nxt;

} e[MAXN << ];

template <typename T> inline void chkmax(T &x,T y) { x = max(x,y); }

template <typename T> inline void chkmin(T &x,T y) { x = min(x,y); }

template <typename T> inline void read(T &x)

{

    T f = ; x = ;

    char c = getchar();

    for (; !isdigit(c); c = getchar()) if (c == '-') f = -f;

    for (; isdigit(c); c = getchar()) x = (x << ) + (x << ) + c - '';

    x *= f;

}

inline void addedge(int u,int v)

{

        tot++;

        e[tot] = (edge){v,head[u]};

        head[u] = tot;

}

inline double dp(int u,int fa)

{

        int cnt = ;

        if (visited[u]) return f[u];

        for (int i = head[u]; i; i = e[i].nxt)

        {

                int v = e[i].to;

                if (v == fa) continue;

                cnt++;

        }

        if (cnt == )

        {

                visited[u] = true;

                return f[u] = ;

        }

        f[u] = ;

        for (int i = head[u]; i; i = e[i].nxt)

        {

                int v = e[i].to;

                if (v == fa) continue;

                f[u] += 1.0 / cnt * dp(v,u);

        }

        visited[u] = true;

        return f[u];

}

int main()

{

        read(n);

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

        {

                int u , v;

                read(u); read(v);

                addedge(u,v);

                addedge(v,u);

        }

        memset(visited,false,sizeof(visited));

        printf("%.10lf\n",dp(,));

        return ;

}