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 MAXN = 200000;
int n, root;
vector<int> adj[MAXN + 2];
int dfs(int u, int p = -1) {
  set<int> s;
  for (int i = 0; i < (int)adj[u].size(); ++i) {
    int v = adj[u][i];
    if (v != p) {
      int tmp = dfs(v, u);
      if (tmp == -1) return -1;
      s.insert(tmp + 1);
    }
  }
  if (s.empty()) {
    return 0;
  }
  if ((int)s.size() == 1) {
    return *(s.begin());
  }
  if (u != root || (int)s.size() > 2) {
    return -1;
  }
  set<int>::iterator it = s.begin();
  int res = *it;
  ++it;
  res += *it;
  return res;
}
int main() {
  scanf("%d", &n);
  for (int i = 1, u, v; i < n; ++i) {
    scanf("%d %d", &u, &v);
    adj[u].push_back(v);
    adj[v].push_back(u);
  }
  for (int i = 1; i <= n; ++i) {
    if ((int)adj[i].size() > 2) {
      root = i;
      break;
    }
  }
  if (root == 0) {
    --n;
    while (!(n & 1)) {
      n >>= 1;
    }
    printf("%d\n", n);
    return 0;
  }
  int res = dfs(root);
  while (!(res & 1)) res >>= 1;
  printf("%d\n", res);
  return 0;
}
