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>
const int N = 1e6 + 10;
const unsigned long long base = 163;
const int INF = 0x3f3f3f3f;
using namespace std;
vector<int> vec[N];
int root = -1;
int dfs(int u, int fa) {
  set<int> s;
  for (auto v : vec[u]) {
    if (v != fa) {
      int tmp = dfs(v, u);
      if (tmp == -1)
        return -1;
      else
        s.insert(tmp + 1);
    }
  }
  if (s.size() == 0)
    return 0;
  else if (s.size() == 1)
    return *s.begin();
  else if (s.size() == 2 && fa == 0)
    return *s.begin() + *s.rbegin();
  else if (s.size() == 2 && fa != 0) {
    root = u;
    return -1;
  } else
    return -1;
}
int main() {
  int n;
  scanf("%d", &n);
  for (int i = 1; i <= n - 1; i++) {
    int u, v;
    scanf("%d%d", &u, &v);
    vec[u].push_back(v), vec[v].push_back(u);
  }
  int ans = dfs(1, 0);
  if (ans == -1 && root != -1) ans = dfs(root, 0);
  while (ans % 2 == 0) ans /= 2;
  cout << ans;
  return 0;
}
