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.*;
import java.io.*;

public class B {
	FastScanner in;
	PrintWriter out;

	int n;
	ArrayList<Integer>[] g;
	
	public void solve() throws IOException {
		n = in.nextInt();
		g = new ArrayList[n];
		for (int i = 0; i < n; i++) {
			g[i] = new ArrayList<>();
		}
		for (int i = 0; i < n - 1; i++) {
			int u = in.nextInt() - 1;
			int v = in.nextInt() - 1;
			g[u].add(v);
			g[v].add(u);
		}
		int[] d = new int[n];
		Arrays.fill(d, -1);
		ArrayDeque<Integer> q = new ArrayDeque<>();
		for (int i = 0; i < n; i++) {
			if (g[i].size() == 1) {
				d[i] = 0;
				q.add(i);
			}
		}
		int cntVerts = n;
		int[] prev = new int[n];
		Arrays.fill(prev, -1);
		boolean[] was = new boolean[n];
		int[] cntWait = new int[n];
		while (!q.isEmpty()) {
			int v = q.poll();
			int toGo = -1;
			boolean manyWays = false;
			for (int u : g[v]) {
				if (!was[u] && u != prev[v]) {
					if (toGo == -1) {
						toGo = u;
					} else {
						manyWays = true;
						break;
					}
				}
			}
			if (manyWays) {
				d[v] = -1;
				cntWait[v]++;
				if (cntWait[v] > 1) {
					out.println(-1);
					return;
				}
				continue;
			}
			if (toGo == -1) {
				continue;
			}
			// only one way toGo
			if (d[toGo] == d[v] + 1) {
				// already path, eliminate us
				int u = v;
				while (u != -1) {
					was[u] = true;
					cntVerts--;
					u = prev[u];
				}
			} else if (d[toGo] == -1) {
				d[toGo] = d[v] + 1;
				prev[toGo] = v;
				q.add(toGo);
			}
		}
		while (cntVerts > 1 && cntVerts % 2 != 0) {
			cntVerts = (cntVerts - 1) / 2 + 1;
		}
		out.println(cntVerts - 1);
	}

	public void run() {
		try {
			in = new FastScanner();
			out = new PrintWriter(System.out);

			solve();

			out.close();
		} catch (IOException e) {
			e.printStackTrace();
		}
	}

	class FastScanner {
		BufferedReader br;
		StringTokenizer st;

		FastScanner() {
			br = new BufferedReader(new InputStreamReader(System.in));
		}

		String next() {
			while (st == null || !st.hasMoreTokens()) {
				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());
		}
	}

	public static void main(String[] arg) {
		new B().run();
	}
}