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 inf = 1.01e9;
const double eps = 1e-9;
const int N = 2e5 + 10;
vector<int> v[N];
set<int> s[N];
int dead[N];
int deg[N];
int main() {
  int n;
  cin >> n;
  for (int i = 0; i < n - 1; i++) {
    int x, y;
    cin >> x >> y;
    x = x - 1;
    y = y - 1;
    v[x].push_back(y);
    v[y].push_back(x);
  }
  for (int i = 0; i < n; i++) deg[i] = ((int)(v[i]).size());
  set<pair<pair<int, int>, int>> S;
  for (int i = 0; i < n; i++) S.insert({{deg[i], ((int)(s[i]).size())}, i});
  int res = -1;
  for (int it = 0; it < n; it++) {
    int x = S.begin()->second;
    S.erase(S.begin());
    if (it == n - 1) {
      vector<int> z;
      for (int y : s[x]) z.push_back(y);
      if (((int)(z).size()) == 1)
        res = z[0];
      else if (((int)(z).size()) == 2)
        res = z[0] + z[1];
      break;
    }
    dead[x] = 1;
    int len = 0;
    if (((int)(s[x]).size()) > 1) break;
    if (((int)(s[x]).size()) == 1) len = *s[x].begin();
    int y = -1;
    for (int z : v[x])
      if (!dead[z]) y = z;
    S.erase({{deg[y], ((int)(s[y]).size())}, y});
    deg[y]--;
    s[y].insert(len + 1);
    S.insert({{deg[y], ((int)(s[y]).size())}, y});
  }
  if (res >= 0) {
    while (res % 2 == 0) res /= 2;
    cout << res << endl;
  } else
    puts("-1");
  return 0;
}
