Example

Input

5
1 2
1 3
1 4
1 5


Output

6
#include <bits/stdc++.h>

using namespace std;
using ll = long long;
#define int ll
using VI = vector<int>;
using VVI = vector<VI>;
using PII = pair<int, int>;

#define FOR(i, a, n) for (ll i = (ll)a; i < (ll)n; ++i)
#define REP(i, n) FOR(i, 0, n)
#define ALL(x) x.begin(), x.end()
#define PB push_back

const ll LLINF = (1LL<<60);
const int INF = (1LL<<30);
const int MOD = 1000000007;

template <typename T> T &chmin(T &a, const T &b) { return a = min(a, b); }
template <typename T> T &chmax(T &a, const T &b) { return a = max(a, b); }
template <typename T> bool IN(T a, T b, T x) { return a<=x&&x<b; }
template<typename T> T ceil(T a, T b) { return a/b + !!(a%b); }
template<class S,class T>
ostream &operator <<(ostream& out,const pair<S,T>& a){
  out<<'('<<a.first<<','<<a.second<<')';
  return out;
}
template<class T>
ostream &operator <<(ostream& out,const vector<T>& a){
  out<<'[';
  REP(i, a.size()) {out<<a[i];if(i!=a.size()-1)out<<',';}
  out<<']';
  return out;
}

int dx[] = {0, 1, 0, -1}, dy[] = {1, 0, -1, 0};

int b = 1007, mo = 1e9+7;
VI g[100010];
map<int,int> v;
// 部分木xのハッシュを返す
int func(int x, int p) {
  int ret = b;
  for(int e: g[x]) {
    if(e == p) continue;
    (ret += func(e, x) * b % mo) %= mo;
  }
  v[ret]++;
  return ret;
}

signed main(void)
{
  cin.tie(0);
  ios::sync_with_stdio(false);

  int n;
  cin >> n;
  REP(i, n-1) {
    int a, b;
    cin >> a >> b; a--, b--;
    g[a].PB(b);
    g[b].PB(a);
  }

  mo = 1e9+7;
  b = rand() % mo;
  v.clear();
  func(0, -1);

  int ret = 0;
  for(auto i: v) ret += i.second*(i.second-1)/2;
  cout << ret << endl;

  return 0;
}

