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.*;
public class A {
    public static void main(String[] args)throws Throwable {
        MyScanner sc=new MyScanner();
        PrintWriter pw=new PrintWriter(System.out);

        n=sc.nextInt();
        adj=new ArrayList[n];
        TreeSet<Integer> [] val=new TreeSet[n];
        for(int i=0;i<n;i++){
            adj[i]=new ArrayList<>();
            val[i]=new TreeSet<>();
        }
        deg=new int [n];
        for(int i=0;i<n-1;i++){
            int u=sc.nextInt()-1;
            int v=sc.nextInt()-1;
            deg[u]++;
            deg[v]++;
            adj[u].add(v);
            adj[v].add(u);
        }
        PriorityQueue<pair> q=new PriorityQueue<>();
        boolean [] removed=new boolean [n];
        for(int i=0;i<n;i++)
            if(deg[i]==1) {
                q.add(new pair(i,0));
                val[i].add(0);
            }
        boolean ok=true;
        lop : while (!q.isEmpty()){
            pair p=q.poll();
            for(int v : adj[p.node])
                if(!removed[v]){
                    removed[p.node]=true;
                    val[v].add(p.val+1);
                    val[p.node].clear();
                    if(val[v].size()>2){
                        ok=false;
                        break lop;
                    }
                    deg[v]--;
                    if(deg[v]==1 && val[v].size()==1)
                        q.add(new pair(v,val[v].first()));
                    break;
                }
        }
        int ans=0;
        for(int i=0;i<n;i++)
            if(!val[i].isEmpty()){
                if(ans>0)
                    ok=false;
                for(int x : val[i])
                    ans+=x;
            }
        if(!ok)
            pw.println(-1);
        else{
            while(ans%2==0)
                ans/=2;
            pw.println(ans);
        }

        pw.flush();
        pw.close();
    }
    static int n;
    static int [] deg;
    static ArrayList<Integer> [] adj;

    static class pair implements Comparable<pair>{
        int node,val;

        pair(int n,int v){
            node=n;
            val=v;
        }

        public int compareTo(pair p){
            return val-p.val;
        }
    }

    static class MyScanner {
        BufferedReader br;
        StringTokenizer st;
        public MyScanner() {
            br = new BufferedReader(new InputStreamReader(System.in));
        }
        String next() {while (st == null || !st.hasMoreElements()) {
            try {st = new StringTokenizer(br.readLine());}
            catch (IOException e) {e.printStackTrace();}}
            return st.nextToken();}
        int nextInt() {return Integer.parseInt(next());}
        long nextLong() {return Long.parseLong(next());}
        double nextDouble() {return Double.parseDouble(next());}
        String nextLine(){String str = "";
            try {str = br.readLine();}
            catch (IOException e) {e.printStackTrace();}
            return str;}
    }
}