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 INF = 0x3f3f3f3f;
const int mod = 1000000007;
int head[200009], nxt[400031], vv[400031], d[200009], dep[200009], fa[200009];
inline void add(int u, int v) {
  static int i = 0;
  vv[i] = v;
  nxt[i] = head[u];
  head[u] = i++;
}
int dfs1(int u, int r) {
  if (d[u] > 2) return u;
  for (int i = head[u]; ~i; i = nxt[i]) {
    if (vv[i] != r) return dfs1(vv[i], u);
  }
  return -1;
}
set<pair<int, pair<int, int>>> s;
inline void f(int u) {
  int v = u;
  while (d[v] < 3) v = fa[v];
  if (!s.emplace(dep[v], make_pair(v, dep[u] - dep[v])).second) --d[v];
}
void dfs(int u, int p) {
  dep[u] = dep[p] + 1;
  fa[u] = p;
  if (d[u] == 1) {
    f(u);
    return;
  }
  for (int i = head[u]; ~i; i = nxt[i]) {
    if (vv[i] != p) dfs(vv[i], u);
  }
}
inline int get(int u) {
  while (fa[u] && d[u] < 3) u = fa[u];
  return u;
}
int main() {
  int n;
  cin >> n;
  int u, v;
  memset(head, -1, sizeof head);
  for (int i = 0; i < n - 1; ++i) {
    scanf("%d%d", &u, &v);
    add(u, v);
    add(v, u);
    ++d[u];
    ++d[v];
  }
  for (int i = 1; i <= n; ++i)
    if (d[i] == 1) {
      u = i;
      break;
    }
  v = dfs1(u, u);
  if (v < 0) {
    int ans = n - 1;
    while (ans % 2 == 0) ans >>= 1;
    cout << ans << endl;
    return 0;
  }
  dfs(v, 0);
  while (s.size() > 2) {
    auto it = s.rbegin(), itt = it;
    ++itt;
    int p = it->second.first, q = itt->second.first;
    if (p == q || p == v) {
      puts("-1");
      return 0;
    }
    int len = it->second.second, r = get(p);
    s.erase(*it);
    if (!s.emplace(dep[r], make_pair(r, dep[p] - dep[r] + len)).second) --d[r];
  }
  int res = 0;
  for (auto& x : s) res += x.second.second;
  while (res % 2 == 0) res >>= 1;
  cout << res << endl;
  return 0;
}
