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 N = 200000;
vector<int> g[N], vv;
int vvv;
int n, z;
void print(int x) {
  if (x == -1)
    cout << x;
  else {
    while (x % 2 == 0) x /= 2;
    cout << x << endl;
  }
  exit(0);
}
int dfs(int v, int p = -1) {
  vector<pair<int, int> > a;
  set<int> s;
  for (auto u : g[v]) {
    if (u == p) continue;
    int x = dfs(u, v);
    if (x == -1) return -1;
    a.push_back({x, u});
    s.insert(x);
  }
  if (a.size() == 0) return 0;
  sort(a.begin(), a.end());
  int q = -1;
  if (s.size() > 2 || (s.size() == 2 && v != vvv))
    for (int i = 0; i + 1 < a.size(); i++)
      if (a[i].first != a[i + 1].first && (vv.size() == 0 || z)) {
        if (!z) vv.push_back(a[i].second);
        if (!z) vv.push_back(a[i + 1].second);
        return -1;
      }
  int x = 0;
  for (auto j : s) x += j;
  return x + s.size();
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cin >> n;
  for (int i = 0; i < n - 1; i++) {
    int u, v;
    cin >> u >> v;
    g[u].push_back(v);
    g[v].push_back(u);
  }
  vvv = 1;
  int ans = dfs(1);
  if (ans == -1) {
    for (auto v : vv) {
      z = 1;
      vvv = v;
      ans = dfs(v);
      if (ans != -1) {
        print(ans);
      }
    }
  }
  print(ans);
}
