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.Iterator;
import java.util.Scanner;
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;
        HashSet<Integer> leaves = new HashSet<>();

        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);
            }
            for (int i = 1; i <= n; i++) {
                if (nodes[i].neighbour.size() == 1) {
                    leaves.add(i);
                }
            }
            boolean flag = true;
            while (flag) {
                flag = false;
                for (int leave : leaves) {
                    if (dfs(leave, new ArrayList<>(), new HashSet<>())) {
                        flag = true;
                        break;
                    }
                }
            }
            int leave = leaves.iterator().next();
            out.println(dfs2(leave, 0));
        }

        int dfs2(int curr, int prev) {
            if (nodes[curr].neighbour.size() > 2) return -1;
            if (prev != 0 && nodes[curr].neighbour.size() == 1) return 0;
            int len = 0;
            for (int next : nodes[curr].neighbour) {
                if (next == prev) continue;
                len = dfs2(next, curr);
                if (len == -1) return -1;
                break;
            }
            return len + 1;
        }

        boolean dfs(int curr, ArrayList<Integer> path, HashSet<Integer> cross) {
            if (cross.size() > 1) return false;
            path.add(curr);
            int len = path.size();
            if (len > 2 && leaves.contains(curr)) {
                if (len % 2 == 0) {
                    path.remove(len - 1);
                    return false;
                }
                int vertex = path.get(len / 2);
                if (cross.size() > 0 && !cross.contains(vertex)) {
                    path.remove(len - 1);
                    return false;
                }
                int afterVertex = path.get(len / 2 + 1);
                nodes[vertex].neighbour.remove(Integer.valueOf(afterVertex));
                leaves.remove(curr);
                return true;
            }
            boolean isCross = nodes[curr].neighbour.size() > 2;
            if (isCross) cross.add(curr);
            for (int next : nodes[curr].neighbour) {
                if (len > 1 && next == path.get(len - 2)) continue;
                if (dfs(next, path, cross)) return true;
            }
            path.remove(len - 1);
            if (isCross) cross.remove(curr);
            return false;
        }

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

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

        }

    }
}

