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 maxn = 2e5 + 10, mod = 1e9 + 7;
const long long inf = 1e18;
vector<int> v[maxn], vec;
int pr[maxn];
bool mark[maxn];
pair<int, int> far(int u, int par = -1) {
  pr[u] = par;
  pair<int, int> ans = {0, u};
  for (int y : v[u]) {
    if (y != par) {
      pair<int, int> p = far(y, u);
      p.first++;
      ans = max(ans, p);
    }
  }
  return ans;
}
int dfs(int u) {
  mark[u] = 1;
  int bf = -1;
  for (int y : v[u]) {
    if (!mark[y]) {
      int num = dfs(y);
      if (bf != -1 && num != bf) cout << -1 << endl, exit(0);
      bf = num;
    }
  }
  return bf + 1;
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  int n;
  cin >> n;
  for (int i = 0; i < n - 1; i++) {
    int a, b;
    cin >> a >> b;
    v[a].push_back(b);
    v[b].push_back(a);
  }
  int A = far(1).second;
  int B = far(A).second;
  int tmp = B;
  while (tmp != -1) {
    vec.push_back(tmp);
    tmp = pr[tmp];
  }
  if (int((vec).size()) & 1) {
    set<int> st;
    int u = vec[int((vec).size()) / 2];
    mark[u] = 1;
    for (int y : v[u]) {
      st.insert(dfs(y) + 1);
    }
    if (int((st).size()) > 2) return cout << -1 << endl, 0;
    int num = (*st.begin()) + (*st.rbegin());
    while (!(num & 1)) num >>= 1;
    cout << num << endl;
  } else {
    int u = vec[int((vec).size()) / 2], w = vec[(int((vec).size()) - 2) / 2];
    mark[u] = mark[w] = 1;
    int A = dfs(u), B = dfs(w);
    cout << A + B + 1 << endl;
  }
  return 0;
}
