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;
const long long mod = 1000000007;
vector<int> g[200010];
int d[200010];
vector<int> ps[200010];
bool vis[200010];
void imp() {
  cout << "-1\n";
  exit(0);
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(nullptr);
  int N, u, v, res = 0;
  cin >> N;
  if (N == 2) {
    cout << "1\n";
    return 0;
  }
  for (int i = 1; i < N; i++) {
    cin >> u >> v;
    u--, v--;
    d[u]++;
    d[v]++;
    g[u].push_back(v);
    g[v].push_back(u);
  }
  queue<int> q;
  for (int i = 0; i < N; i++) {
    if (d[i] == 1) {
      q.push(i);
      ps[i] = {0};
      vis[i] = true;
    }
  }
  vector<int> ends;
  while (!q.empty()) {
    u = q.front();
    q.pop();
    bool end = true;
    for (auto v : g[u]) {
      if (vis[v]) continue;
      end = false;
      bool f = false;
      for (int i = 0; i < (int)ps[v].size(); i++) {
        f |= ps[v][i] == ps[u][0] + 1;
      }
      if (!f) ps[v].push_back(ps[u][0] + 1);
      d[v]--;
      if (d[v] == 1) {
        q.push(v);
        vis[v] = true;
      }
    }
    if (end) {
      ends.push_back(u);
    }
  }
  bool can = q.empty() && ends.size() == 2;
  int cnt = 0;
  for (int i = 0; i < N; i++) {
    can &= vis[i] && ps[i].size() <= 2;
    cnt += ps[i].size() > 1;
  }
  if (!can) imp();
  can &= cnt <= 1;
  can &= ps[ends[0]].size() + ps[ends[1]].size() <= 3;
  u = -1;
  if (ps[ends[0]].size() == 1) {
    ps[ends[1]].push_back(ps[ends[0]][0] + 1);
    u = ends[1];
  } else {
    ps[ends[0]].push_back(ps[ends[1]][0] + 1);
    u = ends[0];
  }
  if (u == -1) imp();
  sort(ps[u].begin(), ps[u].end());
  auto it = unique(ps[u].begin(), ps[u].end());
  ps[u].erase(it, ps[u].end());
  can &= ps[u].size() <= 2;
  if (!can) imp();
  for (auto l : ps[u]) res += l;
  while (!(res & 1)) {
    res >>= 1;
  }
  cout << res << '\n';
  return 0;
}
