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

// package CF;

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.StringTokenizer;

public class A {
	static int newRoot;
	static ArrayList<Integer> [] adj;
	static int dfs(int u, int p){
		int len = 0;
		for(int v:adj[u]){
			if(v != p){
				int vv = dfs(v, u);
				if(vv == -1)
					return -1;
				if(len == 0 || vv == len)
					len = vv;
				else{
					newRoot = u;
					return -1;
				}
			}
		}
		return len+1;
	}
	static int dfsRoot(int u){
		int len1 = 0, len2 = 0;
		for(int v:adj[u]){
			int vv = dfs(v, u);
			if(vv == -1)
				return -1;
			if(len1 == 0 || vv == len1)
				len1 = vv;
			else if(len2 == 0 || vv == len2)
				len2 = vv;
			else
				return -1;
		}
		return len1 + len2 + 1;
	}
	public static void main(String[] args) throws Exception {
		Scanner sc = new Scanner(System.in);
		PrintWriter out = new PrintWriter(System.out);
		int n = sc.nextInt();
		adj = new ArrayList[n];
		for (int i = 0; i < adj.length; ++i) {
			adj[i] = new ArrayList<>();
		}
		for (int i = 0; i < n-1; ++i) {
			int u = sc.nextInt()-1, v = sc.nextInt()-1;
			adj[u].add(v);
			adj[v].add(u);
		}
		int ans = dfsRoot(0);
		if(ans == -1)
			ans = dfsRoot(newRoot);
		if(ans == -1)
			out.println(-1);
		else 
		{
			--ans;
			if(ans != 0)
				while(ans % 2 == 0)
					ans /= 2;
			out.println(ans);
		}
		out.flush();
		out.close();
	}
	
	static class Scanner {
		StringTokenizer st;
		BufferedReader br;

		public Scanner(InputStream s) {
			br = new BufferedReader(new InputStreamReader(s));
		}

		public Scanner(FileReader fileReader) {
			br = new BufferedReader(fileReader);
		}

		public String next() throws IOException {
			while (st == null || !st.hasMoreTokens())
				st = new StringTokenizer(br.readLine());
			return st.nextToken();
		}

		public int nextInt() throws IOException {
			return Integer.parseInt(next());
		}

		public long nextLong() throws IOException {
			return Long.parseLong(next());
		}

		public String nextLine() throws IOException {
			return br.readLine();
		}

		public boolean ready() throws IOException {
			return br.ready();
		}
	}
}