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 double EPS = 1e-6;
const int MOD = 1000000007;
vector<vector<int> > v;
vector<set<int> > lens;
vector<int> deg, used;
int n;
int solve() {
  int res = -1;
  queue<int> q;
  lens.resize(n);
  deg.resize(n);
  used.resize(n);
  for (int i = 0; i < n; i++) deg[i] = v[i].size();
  for (int i = 0; i < n; i++)
    if (deg[i] == 1) {
      lens[i].insert(0);
      q.push(i);
    }
  int cnt = 0;
  int cur;
  while (!q.empty()) {
    cur = q.front();
    q.pop();
    used[cur] = true;
    cnt++;
    if (deg[cur] != 1) continue;
    if (lens[cur].size() != 1) break;
    int value = *lens[cur].begin();
    for (int i = 0; i < v[cur].size(); i++) {
      int to = v[cur][i];
      if (used[to]) continue;
      deg[to]--;
      lens[to].insert(value + 1);
      if (deg[to] == 1) q.push(to);
    }
  }
  if (cnt != n) return -1;
  if (lens[cur].size() > 2) return -1;
  res = accumulate(lens[cur].begin(), lens[cur].end(), 0);
  while (res % 2 == 0) res /= 2;
  return res;
}
int main() {
  scanf("%d", &n);
  v.resize(n);
  for (int i = 0; i < n - 1; i++) {
    int a, b;
    scanf("%d%d", &a, &b);
    a--;
    b--;
    v[a].push_back(b);
    v[b].push_back(a);
  }
  printf("%d\n", solve());
}
