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;
int n;
set<int> tree[200010];
void no() {
  puts("-1");
  exit(0);
}
bool foi = 0;
int calc(int v, int p = -1) {
  int crt = 0;
  set<int> tm;
  vector<int> eli;
  for (auto &it : tree[v]) {
    if (it != p) {
      int tam = calc(it, v);
      if (tm.find(tam) != tm.end()) {
        tree[it].clear();
        eli.push_back(it);
      }
      tm.insert(tam);
    }
  }
  for (int i = 0; i < ((int)(eli).size()); i++) {
    tree[v].erase(eli[i]);
  }
  if (p != -1) {
    if (((int)(tree[v]).size()) == 2)
      return (*tm.begin()) + 1;
    else if (((int)(tree[v]).size()) == 1)
      return 1;
    else if (((int)(tree[v]).size()) == 3) {
      foi = 1;
      return 1e9;
    } else
      no();
  }
}
int desce(int v, int p) {
  set<int> tm;
  for (auto &it : tree[v]) {
    if (it != p) {
      int tam = desce(it, v);
      if (tam == -1) return -1;
      tm.insert(tam);
    }
  }
  if (((int)(tm).size()) == 0)
    return 1;
  else if (((int)(tm).size()) > 1)
    return -1;
  else
    return (*tm.begin()) + 1;
}
int solve(int v, int p = -1) {
  set<int> tm;
  for (auto &it : tree[v]) {
    int tam = desce(it, v);
    if (tam == -1) return -1;
    tm.insert(tam);
  }
  if (((int)(tm).size()) == 2) {
    int tot = 0;
    for (auto &it : tm) tot += it;
    return tot;
  } else if (((int)(tm).size()) == 1) {
    return (*tm.begin());
  }
  return -1;
}
int main() {
  ios_base::sync_with_stdio(false);
  cin >> n;
  for (int i = 1; i < n; i++) {
    int a, b;
    cin >> a >> b;
    --a;
    --b;
    tree[a].insert(b);
    tree[b].insert(a);
  }
  if (n == 2) {
    puts("1");
    return 0;
  }
  calc(0);
  int cnt = 0;
  for (int i = 0; i < n; i++) {
    if (((int)(tree[i]).size()) > 3) no();
    if (((int)(tree[i]).size()) == 3 && cnt > 0) no();
    if (((int)(tree[i]).size()) == 3) cnt = i + 1;
  }
  cerr << cnt << '\n';
  if (cnt == 0) cnt++;
  int ans = solve(cnt - 1);
  while (ans % 2 == 0) ans /= 2;
  cout << ans << '\n';
}
