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 lli = long long int;
using pii = pair<int, int>;
using vi = vector<int>;
using vb = vector<bool>;
using vvi = vector<vector<int>>;
using vlli = vector<long long int>;
using vpii = vector<pair<int, int>>;
int n, u, v, x, far, s, dia, ans, res, minm, ROOT;
vvi adj;
vi dist, root, depth;
bool check;
void dfs_dia(int u, int prev, int far) {
  if (far > dia) {
    dia = far;
    s = u;
  }
  for (auto v : adj[u])
    if (v != prev) {
      dist[v] = max(dist[v], far + 1);
      dfs_dia(v, u, far + 1);
    }
}
void dfs(int u, int prev) {
  set<int> d;
  for (auto v : adj[u])
    if (v != prev) {
      dfs(v, u);
      depth[u] = max(1 + depth[v], depth[u]);
    }
  for (auto v : adj[u])
    if (v != prev) d.insert(depth[v]);
  if (d.size() >= 3)
    check = false;
  else if (d.size() == 2 && u != ROOT)
    check = false;
  else if (u == ROOT && check) {
    dia = 0;
    for (auto x : d) dia += (x + 1);
    while (!(dia % 2)) dia /= 2;
    res = min(res, dia);
  }
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  cin >> n;
  adj.resize(n + 1);
  dist.assign(n + 1, 0);
  minm = 0x3f3f3f3f;
  dia = -0x3f3f3f3f;
  res = 0x3f3f3f3f;
  for (int i = 0; i < n - 1; i++) {
    cin >> u >> v;
    adj[u].push_back(v);
    adj[v].push_back(u);
  }
  dfs_dia(1, -1, 0);
  dfs_dia(s, -1, 0);
  dfs_dia(s, -1, 0);
  for (int i = 1; i <= n; i++) minm = min(minm, dist[i]);
  for (int i = 1; i <= n; i++)
    if (dist[i] == minm) root.push_back(i);
  for (int i = 0; i < root.size(); i++) {
    check = true;
    depth.assign(n + 1, 0);
    ROOT = root[i];
    dfs(root[i], -1);
  }
  if (res == 0x3f3f3f3f)
    cout << -1;
  else
    cout << res;
}
