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 = 2 * 100000;
vector<int> g[MAXN + 1];
int used[MAXN + 1], ptr[MAXN + 1], deg[MAXN + 1], was[MAXN + 1];
int main() {
  int n;
  cin >> n;
  for (int i = 0; i < n - 1; i++) {
    int a, b;
    scanf("%d%d", &a, &b);
    g[a].push_back(b);
    g[b].push_back(a);
  }
  set<pair<int, int> > s;
  for (int i = 1; i <= n; i++) {
    if ((int)g[i].size() == 1) s.insert({1, i});
    deg[i] = (int)g[i].size();
  }
  set<pair<int, int> > ss;
  for (int t = 0; !s.empty(); t++) {
    int v = s.begin()->second;
    int cnt = s.begin()->first;
    if (deg[v] != 1 || used[v]) {
      ss.insert({cnt, v});
      s.erase(s.begin());
      continue;
    }
    used[v] = 1;
    for (int i = ptr[v]; i < (int)g[v].size(); i++, ptr[v]++) {
      int u = g[v][i];
      if (!used[u]) {
        s.erase(s.begin());
        if (s.find(make_pair(cnt + 1, u)) != s.end() ||
            (deg[v] == 1 && !was[u])) {
          if (s.find(make_pair(cnt + 1, u)) == s.end()) was[u] = 1;
          deg[u]--;
        }
        s.insert({cnt + 1, u});
      }
    }
  }
  if ((int)ss.size() > 2) {
    cout << "-1\n";
  } else {
    int res = 0;
    for (auto it : ss) res += it.first - 1;
    while (res % 2 == 0) res /= 2;
    cout << res << "\n";
  }
  return 0;
}
