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 INF = 1e9 + 7;
int ans = INF;
int better(int n) {
  while (n != 0 && n % 2 == 0) n /= 2;
  return n;
}
int minb(int a, int b) { return min(better(a), better(b)); }
vector<vector<int> > g;
vector<int> one;
vector<pair<int, int> > two;
void dfs1(int v, int prev) {
  map<int, int> am;
  for (int u : g[v]) {
    if (u == prev) continue;
    dfs1(u, v);
    am[one[u] + 1]++;
  }
  if (am.size() > 2) {
    one[v] = -1;
  } else if (am.size() == 1) {
    one[v] = (*(am.begin())).first;
    if (one[v] == 0) one[v] = -1;
  } else if (am.size() == 0) {
    one[v] = 0;
  } else {
    one[v] = -1;
    two[v] = make_pair((*(am.begin())).first, (*(++am.begin())).first);
    if (two[v].first == 0 || two[v].second == 0) {
      two[v].second = -1;
      two[v].first = -1;
    }
  }
}
void dfs(int v, int prev, int c) {
  if (one[v] != -1) {
    ans = minb(ans, one[v] + c);
    if (one[v] == c) ans = minb(ans, one[v]);
  }
  if (prev == -1 && two[v] != make_pair(-1, -1)) {
    ans = minb(ans, two[v].first + two[v].second);
  }
  if (two[v] != make_pair(-1, -1) &&
      (two[v].first == c || two[v].second == c)) {
    ans = minb(ans, two[v].first + two[v].second);
  }
  map<int, int> am;
  for (int u : g[v]) {
    if (u != prev) am[one[u] + 1]++;
  }
  for (int u : g[v]) {
    if (u == prev) continue;
    am[one[u] + 1]--;
    if (am[one[u] + 1] == 0) am.erase(one[u] + 1);
    if (am.size() == 1 && ((*(am.begin())).first == c || c == 0) &&
        ((*(am.begin())).first) != 0) {
      dfs(u, v, (*(am.begin())).first + 1);
    }
    am[one[u] + 1]++;
  }
}
int main() {
  int n;
  cin >> n;
  g.resize(n);
  one.resize(n, -1);
  two.resize(n, make_pair(-1, -1));
  for (int i = 1; i < n; ++i) {
    int u, v;
    cin >> u >> v;
    u--;
    v--;
    g[u].push_back(v);
    g[v].push_back(u);
  }
  dfs1(0, -1);
  dfs(0, -1, 0);
  if (ans == INF)
    cout << "-1\n";
  else
    cout << ans << endl;
}
