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.BufferedReader;
import java.io.FileNotFoundException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.StringTokenizer;

/**
 * #
 * 
 * @author pttrung
 */
public class C_Round_397 {

	public static long MOD = 1000000007;
	private static int top = -1;

	public static void main(String[] args) throws FileNotFoundException {
		// PrintWriter out = new PrintWriter(new FileOutputStream(new File(
		// "output.txt")));
		PrintWriter out = new PrintWriter(System.out);
		Scanner in = new Scanner();
		int n = in.nextInt();
		ArrayList<Integer>[] map = new ArrayList[n];
		int start = -1;
		for (int i = 0; i < n; i++) {
			map[i] = new ArrayList<>();
		}
		for (int i = 0; i < n - 1; i++) {
			int u = in.nextInt() - 1;
			int v = in.nextInt() - 1;
			map[u].add(v);
			map[v].add(u);
			if (map[u].size() > 2) {
				start = u;
			} else if (map[v].size() > 2) {
				start = v;
			}
		}

		// System.out.println(start);
		if (start == -1) {
			int l = n - 1;
			while (l % 2 == 0) {
				l /= 2;
			}
			out.println(l);
		} else {
			int[] h = new int[n];
			maxHeight(start, start, h, map);
			if (cal(start, start, 0, h, map)) {
				if (top != -1) {
					maxHeight(top, top, h, map);
					int x = -1, y = -1;
					for (int i : map[top]) {
						if (x == -1) {
							x = h[i];
						} else if (x != h[i] && y == -1) {
							y = h[i];
						}
					}
					int l = x;
					if (y != -1) {
						l += y;
					}
					while (l % 2 == 0) {
						l /= 2;
					}
					out.println(l);
				} else {
					int x = -1, y = -1;
					for (int i : map[start]) {
						if (x == -1) {
							x = h[i];
						} else if (x != h[i] && y == -1) {
							y = h[i];
						}
					}
					int l = x;
					if (y != -1) {
						l += y;
					}
					while (l % 2 == 0) {
						l /= 2;
					}
					out.println(l);
				}
			} else {
				out.println(-1);
			}
		}
		out.close();
	}

	static boolean cal(int index, int pa, int prev, int[] h, ArrayList<Integer>[] map) {
		// System.out.println(index + " " + pa + " " + prev);
		int x = -1;
		int y = -1;

		for (int i : map[index]) {
			if (i != pa) {

				if (x == -1) {
					x = h[i];
				} else if (x != h[i] && y == -1) {
					y = h[i];
				} else if (x != h[i] && y != h[i]) {
					return false;
				}
			}
		}
		// System.out.println(x + " " + y + " " + prev + " " + index);
		if (index == pa) {
			for (int i : map[index]) {
				if (h[i] == x) {
					if (!cal(i, index, y + 1, h, map)) {
						return false;
					}
				} else if (!cal(i, index, x + 1, h, map)) {
					return false;
				}
			}
		} else {
			for (int i : map[index]) {
				if (i != pa && !cal(i, index, prev + 1, h, map)) {
					return false;
				}
			}
		}

		if (x != -1 && y != -1 && index != pa) {
			if (x != prev && y != prev) {
				return false;
			} else {
				top = index;
			}
		}

		return true;
	}

	static int maxHeight(int index, int pa, int[] h, ArrayList<Integer>[] map) {
		int re = 1;
		for (int i : map[index]) {
			if (i != pa) {
				re = Integer.max(re, 1 + maxHeight(i, index, h, map));
			}
		}
		return h[index] = re;
	}

	public static int[] KMP(String val) {
		int i = 0;
		int j = -1;
		int[] result = new int[val.length() + 1];
		result[0] = -1;
		while (i < val.length()) {
			while (j >= 0 && val.charAt(j) != val.charAt(i)) {
				j = result[j];
			}
			j++;
			i++;
			result[i] = j;
		}
		return result;

	}

	public static boolean nextPer(int[] data) {
		int i = data.length - 1;
		while (i > 0 && data[i] < data[i - 1]) {
			i--;
		}
		if (i == 0) {
			return false;
		}
		int j = data.length - 1;
		while (data[j] < data[i - 1]) {
			j--;
		}
		int temp = data[i - 1];
		data[i - 1] = data[j];
		data[j] = temp;
		Arrays.sort(data, i, data.length);
		return true;
	}

	public static int digit(long n) {
		int result = 0;
		while (n > 0) {
			n /= 10;
			result++;
		}
		return result;
	}

	public static double dist(long a, long b, long x, long y) {
		double val = (b - a) * (b - a) + (x - y) * (x - y);
		val = Math.sqrt(val);
		double other = x * x + a * a;
		other = Math.sqrt(other);
		return val + other;

	}

	public static class Point implements Comparable<Point> {

		int x, y;

		public Point(int start, int end) {
			this.x = start;
			this.y = end;
		}

		@Override
		public int hashCode() {
			int hash = 5;
			hash = 47 * hash + this.x;
			hash = 47 * hash + this.y;
			return hash;
		}

		@Override
		public boolean equals(Object obj) {
			if (obj == null) {
				return false;
			}
			if (getClass() != obj.getClass()) {
				return false;
			}
			final Point other = (Point) obj;
			if (this.x != other.x) {
				return false;
			}
			if (this.y != other.y) {
				return false;
			}
			return true;
		}

		@Override
		public int compareTo(Point o) {
			return Integer.compare(x, o.x);
		}
	}

	public static class FT {

		long[] data;

		FT(int n) {
			data = new long[n];
		}

		public void update(int index, long value) {
			while (index < data.length) {
				data[index] += value;
				index += (index & (-index));
			}
		}

		public long get(int index) {
			long result = 0;
			while (index > 0) {
				result += data[index];
				index -= (index & (-index));
			}
			return result;

		}
	}

	public static long gcd(long a, long b) {
		if (b == 0) {
			return a;
		}
		return gcd(b, a % b);
	}

	public static long pow(long a, long b) {
		if (b == 0) {
			return 1;
		}
		if (b == 1) {
			return a;
		}
		long val = pow(a, b / 2);
		if (b % 2 == 0) {
			return val * val % MOD;
		} else {
			return val * (val * a % MOD) % MOD;

		}
	}

	static class Scanner {

		BufferedReader br;
		StringTokenizer st;

		public Scanner() throws FileNotFoundException {
			// System.setOut(new PrintStream(new
			// BufferedOutputStream(System.out), true));
			br = new BufferedReader(new InputStreamReader(System.in));
			// br = new BufferedReader(new InputStreamReader(new
			// FileInputStream(new File("input.txt"))));
		}

		public String next() {

			while (st == null || !st.hasMoreTokens()) {
				try {
					st = new StringTokenizer(br.readLine());
				} catch (Exception e) {
					throw new RuntimeException();
				}
			}
			return st.nextToken();
		}

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

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

		public double nextDouble() {
			return Double.parseDouble(next());
		}

		public String nextLine() {
			st = null;
			try {
				return br.readLine();
			} catch (Exception e) {
				throw new RuntimeException();
			}
		}

		public boolean endLine() {
			try {
				String next = br.readLine();
				while (next != null && next.trim().isEmpty()) {
					next = br.readLine();
				}
				if (next == null) {
					return true;
				}
				st = new StringTokenizer(next);
				return st.hasMoreTokens();
			} catch (Exception e) {
				throw new RuntimeException();
			}
		}
	}
}
