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.*;
import java.util.*;
import java.math.*;

public class E {
	public static void main(String[] args) throws IOException {

		/**/
		Scanner sc = new Scanner(new BufferedReader(new InputStreamReader(System.in)));
		/*/
		Scanner sc = new Scanner(new BufferedReader(new InputStreamReader(new FileInputStream("src/e.in"))));
		/**/
		
		int n = sc.nextInt();
		ArrayList<HashSet<Integer>> neigh = new ArrayList<HashSet<Integer>>();
		for (int i = 0; i < n; i++)
			neigh.add(new HashSet<Integer>());
		for (int i = 0; i < n-1; i++) {
			int u = sc.nextInt()-1;
			int v = sc.nextInt()-1;
			neigh.get(u).add(v);
			neigh.get(v).add(u);
		}
		int u = 0;
		ArrayDeque<Integer> q = new ArrayDeque<Integer>();
		q.add(0);
		boolean[] vis = new boolean[n];
		vis[0] = true;
		while (!q.isEmpty()) {
			u = q.removeFirst();
			for (int v : neigh.get(u)) {
				if (!vis[v]) {
					vis[v] = true;
					q.add(v);
				}
			}
		}
		int farthestU = u;
		int[] par = new int[n];
		par[u] = -1;
		q.add(u);
		vis = new boolean[n];
		vis[u] = true;
		while (!q.isEmpty()) {
			u = q.removeFirst();
			for (int v : neigh.get(u)) {
				if (!vis[v]) {
					vis[v] = true;
					q.add(v);
					par[v] = u;
				}
			}
		}
		ArrayList<Integer> path = new ArrayList<Integer>();
		while (u != farthestU) {
			path.add(u);
			u = par[u];
		}
		int chosen = path.get(path.size()/2);
		int[] dist = new int[n];
		vis = new boolean[n];
		vis[chosen] = true;
		HashSet<Integer> allLeafDists = new HashSet<Integer>();
		for (int v1 : neigh.get(chosen)) {
			dist[v1] = 1;
			q.add(v1);
			vis[v1] = true;
			HashSet<Integer> leafDists = new HashSet<Integer>();
			while (!q.isEmpty()) {
				u = q.removeFirst();
				for (int v : neigh.get(u)) {
					if (!vis[v]) {
						dist[v] = dist[u]+1;
						q.add(v);
						vis[v] = true;
					}
				}
				if (neigh.get(u).size() == 1) {
					leafDists.add(dist[u]);
				}
			}
			if (leafDists.size() > 1) {
				allLeafDists.add(-1);
				allLeafDists.add(-2);
				allLeafDists.add(-3);
			} else {
				allLeafDists.add(leafDists.iterator().next());
			}
		}
		if (allLeafDists.size() > 2) {
			System.out.println(-1);
		} else {
			int ans = 0;
			for (int i : allLeafDists)
				ans += i;
			while (ans%2==0)
				ans/=2;
			System.out.println(ans);
		}
	}
}