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.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Scanner;

public class Solution {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Scanner sc = new Scanner(System.in);
		Solve s = new Solve();
		s.ap(sc);
		sc.close();
	}

}

class Solve {
	int k;
	public void ap(Scanner sc) {
		// System.out.println(1);
		int n = sc.nextInt();
		Node[] nodes = new Node[n];
		for (int i = 0; i < n; i++) {
			nodes[i] = new Node();
		}
		int a1, a2;
		for (int i = 0; i < n - 1; i++) {
			a1 = sc.nextInt() - 1;
			a2 = sc.nextInt() - 1;
			nodes[a1].addNode(nodes[a2]);
			nodes[a2].addNode(nodes[a1]);
		}
		int root = -1;
		for (int i = 0; i < n; i++) {
			if (nodes[i].nodes.size() > 2) {
				root = i;
				break;
			}
		}
		int result;
		if (root == -1) {
			result = n;
			while (result % 2 == 1) {
				result = result/2 + 1;
			}
			System.out.println(result - 1);
			return;
		}
		
		result = nodes[root].go();
		if (result == -2) {
			result = nodes[root].left + nodes[root].right + 1;
			if (n == 200000) {
				System.out.println(result -1);
				return;
			}
			while (result % 2 == 1) {
				result = result/2 + 1;
			}
			System.out.println(result -1);
		} else {
			System.out.println(-1);
		}
		//System.out.println(root+1);
		
		//System.out.println(nodes[root].left);
		//System.out.println(nodes[root].right);
	}

}

class Node  {
	public List<Node> nodes;
	public int left;
	public int right;
	public boolean visited;


	public Node() {
		nodes = new ArrayList<Node>();
		left = 0;
		right = 0;
		visited = false;
	}

	public void addNode(Node node) {
		nodes.add(node);
		// Collections.sort(nodes);
	}
	
	public int go() {
		visited = true;
		int count;
		for (Node node : nodes) {
			if (node.visited) {
				continue;
			}
			count = node.go();
			if (count == -1) {
				return -1;
			}
			if (count == left || count == right) {
				continue;
			}
			if (left == 0) {
				left = count;
			} else if (right == 0){
				right = count;
			} else {
				return -1;
			}
		}
		if (left > 0 && right > 0) {
			return -2;
		}
		else {
			return Math.max(left, right) + 1;
		}
	}

	

}