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 int NMAX = 2 * 100000 + 5;
int N;
vector<int> graph[NMAX];
int deg[NMAX];
int whatLen[NMAX];
bool out[NMAX];
queue<int> q;
int main() {
  ios_base ::sync_with_stdio(false);
  cin >> N;
  for (int i = 1; i < N; ++i) {
    int a, b;
    cin >> a >> b;
    graph[a].push_back(b);
    graph[b].push_back(a);
    deg[a]++;
    deg[b]++;
  }
  for (int i = 1; i <= N; ++i)
    if (deg[i] == 1) q.push(i);
  int rem = N;
  int node;
  while (!q.empty()) {
    node = q.front();
    rem--;
    q.pop();
    if (!rem) break;
    bool same = true;
    int val = 0;
    for (auto it : graph[node])
      if (out[it]) {
        if (val == 0)
          val = whatLen[it];
        else if (val != whatLen[it]) {
          same = false;
          break;
        }
      }
    if (!same) {
      cout << "-1\n";
      return 0;
    }
    whatLen[node] = 1 + val;
    out[node] = true;
    deg[node]--;
    for (auto it : graph[node])
      if (!out[it]) {
        deg[it]--;
        if (deg[it] == 1) q.push(it);
      }
  }
  vector<int> vals;
  for (auto it : graph[node])
    if (out[it]) vals.push_back(whatLen[it]);
  sort(vals.begin(), vals.end());
  vals.resize(unique(vals.begin(), vals.end()) - vals.begin());
  if (vals.size() > 2) {
    cout << "-1\n";
    return 0;
  }
  int sum = 0;
  for (auto it : vals) sum += it;
  while (sum % 2 == 0) sum /= 2;
  cout << sum << '\n';
  return 0;
}
