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

#include <bits/stdc++.h>
using namespace std;
const int nmax = 200009;
vector<int> g[nmax];
int len[nmax], answer, i, n, a, b, root, used[nmax];
bool solve(int act, int up) {
  int flag = 1, leave = 1, nr = 0, sum = 0;
  vector<int> now;
  for (int i = 0; i < g[act].size(); ++i) {
    int nxt = g[act][i];
    if (nxt == up) continue;
    if (!solve(nxt, act)) return 0;
    now.push_back(len[nxt]);
    leave = 0;
  }
  if (leave) {
    len[act] = 1;
    return 1;
  }
  for (int i = 0; i < now.size(); ++i) {
    if (used[now[i]]) continue;
    used[now[i]] = 1;
    nr++;
    sum += now[i];
  }
  for (int i = 0; i < now.size(); ++i) used[now[i]] = 0;
  if (act == root) {
    if (nr == 1) {
      len[act] = 1 + sum;
      return 1;
    } else {
      if (nr == 2) {
        len[act] = 1 + sum;
        return 1;
      } else
        return 0;
    }
  } else {
    if (nr == 1) {
      len[act] = 1 + sum;
      return 1;
    } else
      return 0;
  }
}
int main() {
  scanf("%d", &n);
  for (i = 2; i <= n; ++i) {
    scanf("%d", &a);
    scanf("%d", &b);
    g[a].push_back(b);
    g[b].push_back(a);
  }
  answer = n + 1;
  root = 0;
  for (i = 1; i <= n; ++i)
    if (g[i].size() > g[root].size()) root = i;
  if (solve(root, 0)) {
    int x = len[root];
    while (1 < x && x % 2 == 1) x = (1 + x) / 2;
    answer = min(answer, x);
  }
  if (answer == n + 1) answer = 0;
  printf("%d\n", answer - 1);
  return 0;
}
