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 maxn = 200010;
vector<int> G[maxn];
void addEdge(int u, int v) {
  G[u].push_back(v);
  G[v].push_back(u);
}
int invalid = -1;
int root;
int dfs(int u, int pre) {
  if (invalid != -1) {
    return -1;
  }
  int sz = G[u].size();
  set<int> Set;
  for (int i = 0; i < sz; i++) {
    int v = G[u][i];
    if (v == pre) continue;
    int t = dfs(v, u);
    Set.insert(t);
  }
  int res = 1;
  if (Set.size() == 0) {
  } else if (Set.size() == 1) {
    res += *Set.begin();
  } else if (u == root && Set.size() == 2) {
    set<int>::iterator it = Set.begin();
    res += *it;
    it++;
    res += *it;
  } else {
    if (invalid == -1) invalid = u;
  }
  return res;
}
int main() {
  int n;
  cin >> n;
  for (int i = 1; i < n; i++) {
    int u, v;
    scanf("%d %d", &u, &v);
    addEdge(u, v);
  }
  root = 1;
  int ans = dfs(1, 0);
  if (invalid != -1) {
    root = invalid;
    invalid = -1;
    ans = dfs(root, 0);
  }
  if (invalid != -1) {
    puts("-1");
  } else {
    ans--;
    while (ans % 2 == 0) ans >>= 1;
    cout << ans << endl;
  }
  return 0;
}
