/*
*
********************************************************************************************
* AUTHOR : Vijju123 *
* Language: C++14 *
* Purpose: - *
* IDE used: Codechef IDE. *
********************************************************************************************
*
Comments will be included in practice problems if it helps ^^
*/
#include <iostream>
#include<bits/stdc++.h>
using namespace std;
double ans=0;
void DFS(vector<int>arr[],int u, int previous,int level,double p)
{
if(arr[u].size()==1 && u!=1)
{
ans+=level*p;
return;
}
int i;
int denominator=arr[u].size()-1;
if(u==1)denominator++;
for(i=0;i<arr[u].size();i++)
{
if(arr[u][i]!=previous)
DFS(arr,arr[u][i],u,level+1,p/denominator );
}
return;
}
int main() {
// your code goes here
#ifdef JUDGE
freopen("input.txt", "rt", stdin);
freopen("output.txt", "wt", stdout);
#endif
ios_base::sync_with_stdio(0);
cin.tie(NULL);
cout.tie(NULL);
int n;
cin>>n;
vector<int> arr[n+1];
int i,u,v;
for(i=0;i<n-1;i++)
{
cin>>u>>v;
arr[u].push_back(v);
arr[v].push_back(u);
}
//int leaf=0;
DFS(arr,1,0,0,1.0);
//cout<<"leaf and depth is "<<leaf<<" "<<depth<<endl;
cout<<fixed<<setprecision(9)<<ans<<endl;
return 0;
}
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