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;
void FREOPEN() {
  freopen(
      ""
      ".in",
      "r", stdin);
  freopen(
      ""
      ".out",
      "w", stdout);
}
inline double Time() { return (clock() * 1.0) / CLOCKS_PER_SEC; }
const int N = 200500, inf = 1e9 * 2, MOD = 1e9 + 7;
char CH[N];
const long long INF = 1e18;
const int dx[] = {1, -1, 0, 0, -1, 1, -1, 1};
const int dy[] = {0, 0, 1, -1, -1, 1, 1, -1};
set<int> g[N], sz[N];
bool was[N];
void no() {
  cout << -1;
  exit(0);
}
int main() {
  int n;
  cin >> n;
  for (int i = 1; i < n; i++) {
    int x, y;
    scanf("%d %d", &x, &y);
    g[x].insert(y);
    g[y].insert(x);
  }
  if (n == 2) {
    cout << 1;
    return 0;
  }
  vector<int> vs;
  int l = 0;
  for (int i = 1; i <= n; i++)
    if ((int((g[i]).size())) == 1) vs.push_back(i), sz[i].insert(0);
  while (l < (int((vs).size()))) {
    int v = vs[l++];
    if (was[v]) continue;
    was[v] = 1;
    int pr = *g[v].begin();
    int len = (*sz[v].begin()) + 1;
    g[pr].erase(v);
    sz[pr].insert(len);
    if ((int((g[pr]).size())) < 2 && (int((sz[pr]).size())) == 1)
      vs.push_back(pr);
  }
  int root = 0;
  for (int i = 1; i <= n; i++) {
    if (was[i] == 0) {
      if (root) no();
      root = i;
    }
  }
  if ((int((sz[root]).size())) > 2) no();
  int ans = 0;
  for (auto i : sz[root]) ans += i;
  while (ans % 2 == 0) ans /= 2;
  cout << ans;
  return 0;
}
