#include <bits/stdc++.h>
using namespace std;
template <typename T1, typename T2>
istream& operator>>(istream& in, pair<T1, T2>& a) {
  in >> a.first >> a.second;
  return in;
}
template <typename T1, typename T2>
ostream& operator<<(ostream& out, pair<T1, T2> a) {
  out << a.first << " " << a.second;
  return out;
}
template <typename T, typename T1>
T amax(T& a, T1 b) {
  if (b > a) a = b;
  return a;
}
template <typename T, typename T1>
T amin(T& a, T1 b) {
  if (b < a) a = b;
  return a;
}
const long long INF = 1e18;
const int32_t M = 1e9 + 7;
const int32_t MM = 998244353;
const long long N = 2e5 + 5;
set<long long> v[N];
set<long long> d[N];
void solve() {
  long long n;
  cin >> n;
  for (long long i = 1; i < n; i++) {
    long long x, y;
    cin >> x >> y;
    v[x].insert(y);
    v[y].insert(x);
  }
  vector<long long> leaves;
  for (long long i = 1; i < n + 1; i++) {
    if ((long long)((v[i]).size()) == 1) {
      d[i].insert(0);
      leaves.push_back(i);
    }
  }
  long long root = 0;
  while ((long long)((leaves).size())) {
    long long tmp = leaves.back();
    leaves.pop_back();
    long long dep = *d[tmp].begin() + 1;
    long long par = *v[tmp].begin();
    v[par].erase(tmp);
    d[par].insert(dep);
    if ((long long)((d[par]).size()) == 1 &&
        (long long)((v[par]).size()) == 1) {
      leaves.push_back(par);
    }
    if ((long long)((v[par]).size()) == 0) {
      root = par;
      break;
    }
  }
  if (root == 0 || (long long)((d[root]).size()) > 2) {
    cout << -1;
    return;
  }
  long long len = 0;
  for (long long x : d[root]) {
    len += x;
  }
  while (len % 2 == 0) {
    len /= 2;
  }
  cout << len;
}
signed main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  long long t = 1;
  while (t--) solve();
  return 0;
}
