#include <bits/stdc++.h>
using namespace std;
int n;
const int max_=100000;
double ans=0;
vector<int>v[max_];
void dfs(int at, int parent, double probabilty, int d){
int b=0;
for(int i:v[at]){
    if(i!=parent){
        b++;
    }
}
for(int i:v[at]){
    if(i!=parent){
        dfs(i, at, probabilty/b, d+1);
    }
}
if(b==0){
    ans+=probabilty*d;
}
}
int main()
{
     cin>>n;
     for(int i=0; i<n-1; i++){
        int a,b;
        cin>>a>>b;
        a--;
        b--;
        v[a].push_back(b);
        v[b].push_back(a);
     }
     dfs(0, 0, 1.0, 0);
    
    printf("%.6lf\n", ans);
    return 0;
}