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 long long mod = 1e9 + 7, siz = 1e6 + 5;
vector<long long> g[siz];
long long t, n, m, k, a[siz], node, dep[siz];
void go(long long u, long long p) {
  dep[u] = 1 + dep[p];
  for (auto v : g[u]) {
    if (v == p) continue;
    go(v, u);
  }
}
long long go2(long long u, long long p) {
  dep[u] = 1 + dep[p];
  long long a = -1;
  long long mx = dep[u];
  for (auto v : g[u]) {
    if (v == p) continue;
    long long cur = go2(v, u);
    mx = max(mx, cur);
    if (a == -1)
      a = cur;
    else if (a == cur)
      continue;
    else if (u != node) {
      cout << -1 << endl;
      exit(0);
    }
  }
  return mx;
}
int32_t main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cin >> n;
  for (long long i = 1; i < n; i++) {
    long long x, y;
    cin >> x >> y;
    g[x].push_back(y);
    g[y].push_back(x);
  }
  go(1, 0);
  for (long long i = 1; i <= n; i++)
    if (dep[i] > dep[node]) node = i;
  memset(dep, 0, sizeof dep);
  go(node, 0);
  long long mx = 0;
  for (long long i = 1; i <= n; i++) mx = max(mx, dep[i] - 1);
  mx /= 2;
  for (long long i = 1; i <= n; i++)
    if (dep[i] - 1 == mx) node = i;
  memset(dep, 0, sizeof dep);
  go(node, 0);
  set<long long> s;
  for (long long i = 1; i <= n; i++) {
    if (g[i].size() > 1) continue;
    s.insert(dep[i] - 1);
  }
  if (s.size() > 2) return cout << -1 << endl, 0;
  memset(dep, 0, sizeof dep);
  go2(node, 0);
  long long ans = *s.begin();
  s.erase(s.begin());
  if (s.size()) ans += *s.begin();
  for (long long i = 0; i <= 20; i++)
    if (ans == (1 << i)) ans = 1;
  cout << ans << endl;
}
