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 N = 100100 * 2;
long long n, vis[N], par[N], p, ans, dia, hdia, tmp, f, leaf[N], sub[N];
set<int> s;
vector<long long> adj[N];
void g(long long u, long long v) {
  adj[u].push_back(v);
  adj[v].push_back(u);
}
void dfs(int u, long long d) {
  sub[u] = 1;
  int lf = 1;
  vis[u] = 1;
  if (d > dia) {
    dia = d;
    hdia = u;
  }
  for (auto o : adj[u])
    if (!vis[o]) {
      lf = 0;
      par[o] = u;
      dfs(o, d + 1);
      sub[u] += sub[o];
    }
  if (lf) leaf[u] = 1;
}
void branch(int u, long long d) {
  vis[u] = 1;
  for (auto o : adj[u]) {
    if (!vis[o]) branch(o, d + 1);
  }
  if (leaf[u] && u != p) s.insert(d);
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  cin >> n;
  for (long long i = 1; i <= n; i++) par[i] = i;
  for (long long i = 1; i <= n - 1; i++) {
    int a, b;
    cin >> a >> b;
    g(a, b);
  }
  dfs(1, 0);
  memset(vis, 0, sizeof vis);
  dia = -1;
  dfs(hdia, 0);
  int k = (dia) / 2, kk = hdia;
  while (k--) {
    kk = par[kk];
  }
  p = kk;
  memset(vis, 0, sizeof vis);
  branch(p, 0);
  if (s.size() <= 2) {
    for (auto o : s) ans += o;
    while (!(ans & 1)) ans /= 2;
    cout << ans << endl;
  } else
    cout << "-1" << endl;
}
