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 INF = INT_MAX;
const int MAX = 200010;
const long long MOD = 1e9 + 7;
int DX[] = {-1, 0, 1, 0};
int DY[] = {0, 1, 0, -1};
vector<vector<int>> G;
int memo[MAX];
int degree[MAX];
long long go(int u, int p) {
  set<long long> s;
  for (auto &v : G[u]) {
    if (v != p) {
      s.insert(go(v, u));
    }
  }
  if (p == -1) {
    if (s.size() == 0) return 0;
    if (s.size() == 1) return (*s.begin());
    if (s.size() == 2) {
      long long ret = 0;
      auto it = s.begin();
      ret += *it;
      ++it;
      ret += *it;
      return ret;
    }
  }
  if (s.size() == 0) return 1;
  if (s.size() == 1) return (*s.begin()) + 1;
  memo[u] = 1;
  return INT_MAX;
}
int main() {
  ios_base::sync_with_stdio(0);
  int n;
  cin >> n;
  G = vector<vector<int>>(n + 1);
  int mx = 0;
  for (int i = 0; i < n - 1; i++) {
    int a, b;
    cin >> a >> b;
    G[a].push_back(b);
    G[b].push_back(a);
    degree[a]++;
    degree[b]++;
    mx = max(mx, max(degree[a], degree[b]));
  }
  long long ans = INT_MAX;
  for (int i = 1; i <= n; i++) {
    if (degree[i] == mx) {
      ans = min(ans, go(i, -1));
      break;
    }
  }
  for (int i = 1; i <= n; i++) {
    if (memo[i] == 1) {
      ans = min(ans, go(i, -1));
      break;
    }
  }
  if (ans >= INT_MAX) ans = -1;
  while (ans % 2 == 0 && ans > 1) ans /= 2;
  cout << ans << "\n";
}
