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 NIL = -1;
template <class T>
inline T mx(T a, T b) {
  return a > b ? a : b;
}
template <class T>
inline T mi(T a, T b) {
  return a < b ? a : b;
}
template <class T>
inline void sw(T &a, T &b) {
  T t = a;
  a = b;
  b = t;
}
template <class T>
inline T mabs(T x) {
  return x < 0 ? -x : x;
}
inline char gc() {
  char ret;
  while ((ret = getchar()) == ' ' || ret == '\n' || ret == '\t')
    ;
  return ret;
}
const int LIM = 2e5 + 10;
vector<int> adj[LIM];
set<int> len[LIM];
int deg[LIM], vis[LIM];
int n, u, v;
inline void bfs() {
  queue<int> q;
  for (int i = 1; i <= n; i++)
    if (deg[i] == 1) len[i].insert(0), q.push(i);
  while (!q.empty()) {
    int x = q.front();
    q.pop(), vis[x] = true;
    vector<int> &t = adj[x];
    for (int i = 0; i < t.size(); i++) {
      if (vis[t[i]]) continue;
      len[t[i]].insert(*len[x].begin() + 1);
      deg[t[i]]--;
      if (deg[t[i]] == 1 && len[t[i]].size() == 1) q.push(t[i]);
    }
  }
}
inline int solve() {
  bfs();
  int cnt = 0;
  for (int i = 1; i <= n; i++) {
    if (len[i].size() > 2) return -1;
    if (len[i].size() == 2) cnt++;
  }
  if (cnt > 1) return -1;
  int ret = 0;
  for (int i = 1; i <= n; i++)
    ret = mx(ret, len[i].size() == 1 ? *len[i].begin()
                                     : *len[i].begin() + *len[i].rbegin());
  while (!(ret & 1)) ret >>= 1;
  return ret;
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(NULL), cout.tie(NULL);
  cin >> n;
  for (int i = 1; i < n; i++) {
    cin >> u >> v;
    adj[u].push_back(v), adj[v].push_back(u);
    deg[u]++, deg[v]++;
  }
  cout << solve();
  return 0;
}
