#include <bits/stdc++.h>
using namespace std;
const int MAXN = 2 * 100000;
vector<int> g[MAXN + 1];
int used[MAXN + 1], ptr[MAXN + 1], deg[MAXN + 1], was[MAXN + 1];
int main() {
  int n;
  cin >> n;
  for (int i = 0; i < n - 1; i++) {
    int a, b;
    scanf("%d%d", &a, &b);
    g[a].push_back(b);
    g[b].push_back(a);
  }
  set<pair<int, int> > s;
  for (int i = 1; i <= n; i++) {
    if ((int)g[i].size() == 1) s.insert({1, i});
    deg[i] = (int)g[i].size();
  }
  set<pair<int, int> > ss;
  for (int t = 0; !s.empty(); t++) {
    int v = s.begin()->second;
    int cnt = s.begin()->first;
    if (deg[v] != 1 || used[v]) {
      ss.insert({cnt, v});
      s.erase(s.begin());
      continue;
    }
    used[v] = 1;
    for (int i = ptr[v]; i < (int)g[v].size(); i++, ptr[v]++) {
      int u = g[v][i];
      if (!used[u]) {
        s.erase(s.begin());
        if (s.find(make_pair(cnt + 1, u)) != s.end() ||
            (deg[v] == 1 && !was[u])) {
          if (s.find(make_pair(cnt + 1, u)) == s.end()) was[u] = 1;
          deg[u]--;
        }
        s.insert({cnt + 1, u});
      }
    }
  }
  if ((int)ss.size() > 2) {
    cout << "-1\n";
  } else {
    int res = 0;
    for (auto it : ss) res += it.first - 1;
    while (res % 2 == 0) res /= 2;
    cout << res << "\n";
  }
  return 0;
}
