#include <bits/stdc++.h>
using namespace std;
struct IO {
  char buf[(1 << 20)], *p1, *p2;
  char pbuf[(1 << 20)], *pp;
  IO() : p1(buf), p2(buf), pp(pbuf) {}
  inline char gc() {
    return getchar();
    if (p1 == p2) p2 = (p1 = buf) + fread(buf, 1, (1 << 20), stdin);
    return p1 == p2 ? ' ' : *p1++;
  }
  inline bool blank(char ch) {
    return ch == ' ' || ch == '\n' || ch == '\r' || ch == '\t';
  }
  template <class T>
  inline void read(T &x) {
    register double tmp = 1;
    register bool sign = 0;
    x = 0;
    register char ch = gc();
    for (; !(ch >= '0' && ch <= '9'); ch = gc())
      if (ch == '-') sign = 1;
    for (; (ch >= '0' && ch <= '9'); ch = gc()) x = x * 10 + (ch - '0');
    if (ch == '.')
      for (ch = gc(); (ch >= '0' && ch <= '9'); ch = gc())
        tmp /= 10.0, x += tmp * (ch - '0');
    if (sign) x = -x;
  }
  inline void read(char *s) {
    register char ch = gc();
    for (; blank(ch); ch = gc())
      ;
    for (; !blank(ch); ch = gc()) *s++ = ch;
    *s = 0;
  }
  inline void read(char &c) {
    for (c = gc(); blank(c); c = gc())
      ;
  }
  template <class t>
  inline void write(t x) {
    if (x < 0)
      putchar('-'), write(-x);
    else {
      if (x > 9) write(x / 10);
      putchar('0' + x % 10);
    }
  }
} io;
const int mod = 1e9 + 7;
const int mo = 998244353;
const int N = 5e5 + 5;
vector<int> g[N];
int n, m, fat[N], dep[N], out[N];
double f[N], Ans;
inline void Dfs(int u, int fa) {
  fat[u] = fa;
  dep[u] = dep[fa] + 1;
  for (int i = (0); i <= ((int)g[u].size() - 1); i++)
    if (g[u][i] ^ fa) Dfs(g[u][i], u);
}
inline void dfs(int u, int fa) {
  int S = (int)g[u].size();
  if (!S) {
    Ans += f[u] * (dep[u] - 1);
    return;
  }
  for (int i = (0); i <= (S - 1); i++) {
    int v = g[u][i];
    f[v] = 1.0 * f[u] / (1.0 * S);
    dfs(v, u);
  }
}
int main() {
  io.read(n);
  for (int i = (1); i <= (n - 1); i++) {
    int x, y;
    io.read(x), io.read(y);
    g[x].push_back(y);
    g[y].push_back(x);
  }
  Dfs(1, 0);
  for (int i = (1); i <= (n); i++) g[i].clear();
  for (int i = (1); i <= (n); i++) g[fat[i]].push_back(i);
  f[1] = 1;
  dfs(1, 0);
  printf("%.15lf\n", Ans);
  return 0;
}
