#include <bits/stdc++.h>
#define int long long
using namespace std;
 
 
 
 
int n;
vector<int> adj[100008];
long double f(int v , int p ){
	long double sum = 0;
	for(auto u : adj[v])
		if(u != p)
			sum += f(u, v) + 1;
	return sum ? sum / (adj[v].size() - (p != -1)) : 0;
}
void solve(){
	cin>>n;
	for(int i=0;i<n-1;i++){
		int x,y;
		cin>>x>>y;
		adj[--x].push_back(--y);
		adj[y].push_back(x);
	}
 
	long double ans=f(0,-1);
	cout << fixed << setprecision(7) << ans << '\n';
 
 
}
 
signed main() {
 
        solve();
 
    return 0;
}
 

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

NAoxIDIKMSAzCjIgNA==

4
1 2
1 3
2 4