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.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.HashSet;
import java.util.AbstractCollection;
import java.util.Scanner;
import java.util.LinkedList;
import java.util.ArrayList;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 *
 * @author Yilin Chen
 */
public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        TaskE solver = new TaskE();
        solver.solve(1, in, out);
        out.close();
    }

    static class TaskE {
        int n;
        Node[] nodes;

        public void solve(int testNumber, Scanner in, PrintWriter out) {
            n = in.nextInt();
            nodes = new Node[n + 10];
            for (int i = 1; i <= n; i++) {
                nodes[i] = new Node(i);
            }
            for (int i = 1; i < n; i++) {
                int a = in.nextInt(), b = in.nextInt();
                nodes[a].neighbour.add(b);
                nodes[b].neighbour.add(a);
            }
            int x = findFarthest(1);
            int y = findFarthest(x);
            int mid = findMid(x, y, new ArrayList<>());
            if (mid == -1) {
                mid = 1;
            }
            HashSet<Integer> depths = new HashSet<>();
            findDepths(mid, depths);
            if (depths.size() > 2) {
                out.println(-1);
            } else {
                int sum = 0;
                for (int len : depths) {
                    sum += len;
                }
                while (sum % 2 == 0) {
                    sum /= 2;
                }
                out.println(sum);
            }
        }

        int findMid(int x, int y, ArrayList<Integer> path) {
            int len = path.size();
            if (x == y) {
                if (len % 2 == 1) return -1;
                else return path.get(len / 2);
            }
            path.add(x);
            for (int next : nodes[x].neighbour) {
                if (len > 0 && next == path.get(len - 1)) continue;
                int ans = findMid(next, y, path);
                if (ans != -1) return ans;
            }
            path.remove(len);
            return -1;
        }

        void findDepths(int start, HashSet<Integer> depths) {
            boolean vis[] = new boolean[n + 10];
            class SearchNode {
                int id;
                int depth;

                public SearchNode(int id, int depth) {
                    this.id = id;
                    this.depth = depth;
                }
            }
            LinkedList<SearchNode> q = new LinkedList<>();
            q.addLast(new SearchNode(start, 0));
            while (!q.isEmpty()) {
                SearchNode curr = q.getFirst();
                q.removeFirst();
                if (vis[curr.id]) continue;
                vis[curr.id] = true;
                if (nodes[curr.id].neighbour.size() == 1) {
                    depths.add(curr.depth);
                }
                for (int next : nodes[curr.id].neighbour) {
                    q.addLast(new SearchNode(next, curr.depth + 1));
                }
            }
        }

        int findFarthest(int start) {
            boolean vis[] = new boolean[n + 10];
            LinkedList<Integer> q = new LinkedList<>();
            q.addLast(start);
            int latest = 0;
            while (!q.isEmpty()) {
                int curr = q.getFirst();
                q.removeFirst();
                if (vis[curr]) continue;
                vis[curr] = true;
                latest = curr;
                for (int next : nodes[curr].neighbour) {
                    q.addLast(next);
                }
            }
            return latest;
        }

        class Node {
            int id;
            ArrayList<Integer> neighbour = new ArrayList<>();

            public Node(int id) {
                this.id = id;
            }

        }

    }
}

