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

import java.io.PrintWriter;
import java.util.Scanner;
import java.util.TreeSet;

public class Eiehn {

  class T {

    final boolean f;
    final int t;

    T(boolean f, int t) {
      this.f = f;
      this.t = t;
    }
  }

  TreeSet<Integer>[] d;

  private void solve(Scanner in, PrintWriter out) {
    int n = in.nextInt();
    d = new TreeSet[n + 1];
    for (int i = 0; i < n; i++) {
      d[i + 1] = new TreeSet<>();
    }
    for (int i = 0; i < n - 1; i++) {
      int a = in.nextInt();
      int b = in.nextInt();
      d[a].add(b);
      d[b].add(a);
    }
    out.println(solve());
  }

  int solve() {
    T x = path(1, -1);
    if (x.f) {
      int t = x.t;
      while (t % 2 == 0) {
        t /= 2;
      }
      return t;
    }

    x = path(x.t, -1);
    if (x.f) {
      int t = x.t;
      while (t % 2 == 0) {
        t /= 2;
      }
      return t;
    }
    return -1;
  }

  T path(int t, int s) {
    TreeSet<Integer> ps = new TreeSet<>();
    Integer[] dt = d[t].toArray(new Integer[d[t].size()]);
    for (int k : dt) {
      if (k == s) {
        continue;
      }
      T x = path(k, t);
      boolean f = x.f;
      int pt = x.t;
      if (!f) {
        return new T(false, pt);
      }
      if (ps.contains(pt)) {
        d[k].remove(t);
        d[t].remove(k);
      }
      ps.add(pt);
    }
    if (s == -1 && ps.size() == 2) {
      return new T(true, ps.stream().mapToInt(Integer::intValue).sum() + 2);
    }
    if (ps.size() > 1) {
      return new T(false, t);
    }
    if (ps.isEmpty()) {
      return new T(true, 0);
    }
    return new T(true, ps.first() + 1);
  }


  public static void main(String[] args) {
    Scanner in = new Scanner(System.in);
    PrintWriter out = new PrintWriter(System.out);
    new Eiehn().solve(in, out);
    in.close();
    out.close();
  }
}
