10
4 2
7 4
2 6
2 5
4 8
10 3
2 9
9 1
5 10
 10
5 10
7 8
8 3
2 6
3 2
9 7
4 5
10 1
6 4
 4
4 1
4 3
4 2
 3
3 1
1 2
 9
1 2
1 3
1 4
1 5
1 6
6 7
6 8
8 9
 5
1 5
2 3
2 4
1 2
 8
6 1
4 7
4 8
8 5
7 6
4 3
4 2
 7
5 6
5 7
5 1
7 4
6 3
3 2
 3
1 3
3 2
 2
1 2
 5
5 4
4 3
3 1
5 2
 6
1 6
3 1
6 4
5 3
2 5
 11
8 9
2 7
1 11
3 2
9 1
8 5
8 6
5 4
4 10
8 3
 11
11 9
6 7
7 1
8 11
5 6
3 5
9 3
10 8
2 4
4 10
 12
12 6
6 7
8 11
4 8
10 4
12 3
2 10
6 2
12 9
4 1
9 5

-1
 9
 1
 1
 3
 3
 -1
 -1
 1
 1
 1
 5
 1
 5
 -1

#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
using u32 = uint32_t;
using vi = vector<int>;
using vvi = vector<vi>;
using vb = vector<bool>;
using vvb = vector<vb>;
using vl = vector<ll>;
using vvl = vector<vl>;
using vd = vector<double>;
using vvd = vector<vd>;
const ll mod = ((ll)1e9) + 7;
int main() {
  cin.tie(0);
  ios_base::sync_with_stdio(false);
  cout << fixed << setprecision(50);
  ll n;
  cin >> n;
  vector<set<ll>> paths(n);
  for (auto i = 0 * (n - 1), i_len = (n - 1); i < i_len; ++i) {
    ll u, v;
    cin >> u >> v;
    u--, v--;
    paths[u].insert(v);
    paths[v].insert(u);
  }
  using P = tuple<ll, ll, ll>;
  function<P(ll, ll, ll)> dfs = [&](ll cur, ll prev, ll depth) {
    if (paths[cur].size() > 2) {
      return P(cur, depth, prev);
    }
    for (ll u : paths[cur])
      if (u != prev) {
        return dfs(u, cur, depth + 1);
      }
    return P(cur, depth, prev);
  };
  vector<set<tuple<ll, ll>>> leafs(n);
  for (auto i = 0 * (n), i_len = (n); i < i_len; ++i)
    if (paths[i].size() == 1) {
      auto p = dfs(i, -1, 0);
      leafs[get<0>(p)].insert(tuple<ll, ll>(get<1>(p), get<2>(p)));
    }
  while (true) {
    bool erased = false;
    for (auto i = 0 * (n), i_len = (n); i < i_len; ++i)
      if (!leafs[i].empty()) {
        if (paths[i].size() <= 2) {
          ll size = get<0>(*leafs[i].begin());
          if (paths[i].size() == 2) {
            size += get<0>(*next(leafs[i].begin()));
          }
          while (size % 2 == 0) size /= 2;
          cout << size << endl;
          return 0;
        }
        auto lhs = leafs[i].begin();
        for (auto it = next(leafs[i].begin()); it != leafs[i].end(); ++it) {
          if (get<0>(*lhs) == get<0>(*it)) {
            paths[i].erase(paths[i].find(get<1>(*lhs)));
            it = leafs[i].erase(lhs);
            erased = true;
          }
          lhs = it;
        }
        if (leafs[i].size() == 1) {
          auto it = leafs[i].begin();
          auto p = dfs(i, get<0>(*it), 0);
          get<1>(p) += get<0>(*it);
          leafs[i].erase(it);
          leafs[get<0>(p)].insert(tuple<ll, ll>(get<1>(p), get<2>(p)));
        }
      }
    if (!erased) {
      cout << -1 << endl;
      return 0;
    }
  }
}
