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 = 200009;
vector<int> e[maxn];
int n, u, v, _root, root, o, tot, d[maxn], q[maxn];
int bfs(int s) {
  int l = 0, r = 0, u;
  memset(d, -1, sizeof d);
  d[s] = 0;
  q[r++] = s;
  while (l < r) {
    u = q[l++];
    for (int j = (0); j <= (e[u].size() - 1); j++)
      if (d[e[u][j]] == -1) {
        d[e[u][j]] = d[u] + 1;
        q[r++] = e[u][j];
      }
  }
  return u;
}
int getMid(int u, int fa, int v) {
  if (u == v) {
    d[u] = 0;
    return tot / 2 == 0;
  }
  int res;
  for (int i = (0); i <= (e[u].size() - 1); i++)
    if (e[u][i] != fa) {
      res = getMid(e[u][i], u, v);
      if (res == -1) continue;
      if (res) return res;
      d[u] = d[e[u][i]] + 1;
    }
  if (d[u] == tot / 2) return u;
  return d[u] == -1 ? -1 : 0;
}
int dfs(int u, int fa) {
  int tmp;
  set<int> s;
  for (int i = (0); i <= (e[u].size() - 1); i++)
    if (e[u][i] != fa) {
      tmp = dfs(e[u][i], u);
      if (tmp == -1) return -1;
      s.insert(tmp);
    }
  if (fa && s.size() >= 2 || !fa && s.size() >= 3) return -1;
  if (fa) return s.empty() ? 1 : *s.begin() + 1;
  int ans;
  if (s.empty())
    ans = 0;
  else if (s.size() == 1)
    ans = *s.begin();
  else
    ans = *s.begin() + *(--s.end());
  while (!(ans & 1)) ans >>= 1;
  return ans;
}
int main() {
  scanf("%d", &n);
  for (int i = (1); i <= (n - 1); i++) {
    scanf("%d%d", &u, &v);
    e[u].push_back(v);
    e[v].push_back(u);
  }
  _root = bfs(1);
  root = bfs(_root);
  tot = d[root];
  memset(d, -1, sizeof d);
  o = getMid(_root, 0, root);
  printf("%d\n", dfs(o, 0));
  return 0;
}
