#include<bits/stdc++.h>
using namespace std;
///////////////////////////////////Nikhil Srivastava////////////////////////////////////////
///////////////////////////////////IIT Jodhpur//////////////////////////////////////////////
///////////////////////////////////Bazinga//////////////////////////////////////////////////
#define SPEED ios::sync_with_stdio(false); cin.tie(0)
#define sci(a) scanf("%d",&a)
#define scl(a) scanf("%I64d",&a)
#define scc(a) scanf("%c",&a)
#define scf(a) scanf("%f",&a)
#define scd(a) scanf("%lf",&a)
#define scs(a) scanf("%s",&a)
#define printi(x) printf("%d\n",x)
#define printl(x) printf("%lld\n",x)
#define loop(i,a,n) for(int i=a;i<n;++i)
#define loopd(i,a,n) for(int i=a;i>=n;--i)
#define nl printf("\n");
#define ll long long int
#define mp(a,b) make_pair(a,b)
#define pi pair < int,int >
#define pl pair < ll,ll >
#define pb push_back
#define maxi 100005
#define MOD (1000000007LL)
#define INF 1e18
#define MAXI 1000005
#define ff first
#define ss second
static int rowNbr[] = {-1, -1, -1, 0, 0, 1, 1, 1};
static int colNbr[] = {-1, 0, 1, -1, 1, -1, 0, 1};
ll power(ll base, ll p){
ll ans = 1;while(p){if(p&1)ans=(ans*base);base=(base*base);p/=2;}return ans;
}
ll modPower(ll base, ll p, ll mod = MOD){
ll ans = 1;while(p){if(p&1)ans=(ans*base)%mod;base=(base*base)%mod;p/=2;}return ans;
}
ll gcd(ll a, ll b){
if(b == 0) return a;
return gcd(b, a%b);
}
/////////////////////////////////////////////Solution From Here//////////////////////////////////////////////////////////
vector<int> adj[MAXI];
bool vis[MAXI];
ll d[MAXI];
long double prob[MAXI];
void bfs(int s)
{
memset(d,0,sizeof(d));
memset(vis,false,sizeof(vis));
deque<int> q;
vis[s] = 1;
d[s] = 0;
prob[s] = 1.0;
q.pb(s);
while(!q.empty()) {
int u = q.front();
q.pop_front();
for(int i=0;i<adj[u].size();++i) {
if(!vis[adj[u][i]]) {
vis[adj[u][i]] = 1;
d[adj[u][i]] = d[u] + 1;
if(u!=1)prob[adj[u][i]] = prob[u]*(1.0/(long double)(adj[u].size()-1));
else prob[adj[u][i]] = prob[u]*(1.0/(long double)(adj[u].size()));
q.pb(adj[u][i]);
}
}
}
}
int main()
{
SPEED;
int n;
cin>>n;
loop(i,1,n) {
int u,v;
cin>>u>>v;
adj[u].pb(v);
adj[v].pb(u);
}
if(n == 1)
{
cout<<"0";
return 0;
}
vector<int> ans;
ans.clear();
loop(i,2,n+1) {
if(adj[i].size() == 1)
ans.pb(i);
}
bfs(1);
long double dd = 0.0;
loop(i,0,ans.size()) {
dd += d[ans[i]]*prob[ans[i]];
}
// cout<<dd;
// long double a = (dd)/(long double)ans.size();
cout<<setprecision(20)<<dd;
}
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