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;
vector<int> adj[200010];
int vis[200010];
int pi[200010];
int depth[200010];
void dfs(int in) {
  vis[in] = 1;
  for (int i = 0; i < adj[in].size(); i++) {
    if (!vis[adj[in][i]]) {
      depth[adj[in][i]] = depth[in] + 1;
      dfs(adj[in][i]);
    }
  }
}
int main() {
  int n;
  scanf("%d", &n);
  for (int i = 1; i < n; i++) {
    int u, v;
    scanf("%d%d", &u, &v);
    adj[u].push_back(v);
    adj[v].push_back(u);
  }
  int start_leaf;
  for (int i = 1; i <= n; i++) {
    if (adj[i].size() == 1) {
      start_leaf = i;
      break;
    }
  }
  dfs(start_leaf);
  int the_odd = 0;
  int max_even_depth = 0;
  for (int i = 1; i <= n; i++) {
    if (adj[i].size() == 1) {
      if (depth[i] % 2 == 0) {
        max_even_depth = max(max_even_depth, depth[i]);
        continue;
      }
      if (the_odd == 0) {
        the_odd = depth[i];
      } else if (depth[i] != the_odd) {
        cout << -1 << endl;
        return 0;
      }
    }
  }
  if (the_odd) {
    for (int i = 1; i <= n; i++) {
      if (depth[i] % 2 == 0 && depth[i] > the_odd) {
        cout << -1 << endl;
        return 0;
      }
    }
    cout << the_odd << endl;
    return 0;
  }
  while (max_even_depth % 2 == 0) {
    max_even_depth /= 2;
  }
  cout << max_even_depth << endl;
  return 0;
}
