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;
long long n, m, root;
vector<long long> a[1000003];
inline int getint() {
  int w = 0, q = 0;
  char c = getchar();
  while ((c < '0' || c > '9') && c != '-') c = getchar();
  if (c == '-') q = 1, c = getchar();
  while (c >= '0' && c <= '9') w = w * 10 + c - '0', c = getchar();
  return q ? -w : w;
}
long long dfs(long long x, long long fa) {
  set<long long> s;
  long long v;
  for (long long i = 0; i <= a[x].size() - 1; i++) {
    v = a[x][i];
    if (v == fa) continue;
    long long val = dfs(v, x);
    if (val == -1) return val;
    s.insert(val + 1);
  }
  if (s.size() == 1) {
    return *s.begin();
  }
  if (s.size() == 0) {
    return 0;
  }
  if (s.size() == 2) {
    if (fa) {
      root = x;
      return -1;
    }
    return *s.begin() + *s.rbegin();
  }
  return -1;
}
int main() {
  long long x, y;
  cin >> n;
  for (long long i = 1; i < n; i++) {
    x = getint(), y = getint();
    a[x].push_back(y), a[y].push_back(x);
  }
  long long ans = dfs(1, 0);
  if (ans == -1 && root) ans = dfs(root, 0);
  while (ans % 2 == 0) ans /= 2;
  cout << ans << endl;
  return 0;
}
