import java.io.*;
import java.util.*;
import java.text.*;
import java.math.*;
import java.util.regex.*;

public class graph {

    int n,e;
    HashMap<Integer,ArrayList<Integer>> list = new HashMap();
    boolean v[];
  static  int distance[];
    
    //Constructor takes input
    graph(){
       
       n = i();      //no of nodes 
       e = n-1;      //no of egdes
       
       
       for(int i=1;i<=n;i++)
       list.put(i,new ArrayList());    
           
           for(int i=0;i<e;i++)               //creating adjacency list
       {
            int a = i();
            int b = i();
           
            list.get(a).add(b);
            list.get(b).add(a);
       }
       
       v = new boolean[n+1];
       cl = new int[n+1];
       distance=new int[n+1]; 
       distance[0]=0; 
    }
    
    public int dfs(int root)
    {
        v[root] = true;
        ArrayList<Integer> ar = list.get(root);
        int c=1;
        for(int i=0;i<ar.size();i++)
        {
            int node = ar.get(i);
            
            
            if(!v[node])      // if element is not visited
            {
                distance[node]=distance[root]+1;
                c+=dfs(node);
            }
        }
        cl[root]=c;
        return c;
    }
    
    static int cl[];    
    
    public static void main(String[] args) {
        
       PrintWriter out=new PrintWriter(System.out); 
       graph g = new graph();
       int root = 1;
       g.dfs(root);
        
       double dd = 0.0d;
       double totaldist=0.0d;
        
       for(int i=2;i<=g.n;i++)
       {
           //System.out.println(i+" "+g.cl[i]+" "+distance[i]);
           dd += (g.n-g.cl[i])*distance[i];
           totaldist+=distance[i];
       }
       
         
        // out.printf("%.14f\n", dd/totaldist);
         System.out.print(dd/totaldist); 
     //  System.out.print(dd/(g.n-1));
    }
    
    
   static Scanner sc = new Scanner(System.in);
  
   static long l(){
        return sc.nextLong();
    }
    static int i(){
        return sc.nextInt();
    }
    static String s(){
        return sc.nextLine();
}
}