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 = 2e5 + 7;
vector<int> E[maxn];
int n, vis[maxn], len[maxn], de[maxn], d[maxn], num[maxn];
pair<int, int> S[maxn];
void ins(int p, int val) {
  if (S[p].first == -1)
    S[p].first = val;
  else if (S[p].first != -1) {
    if (S[p].first != val || S[p].second != val) {
      cout << "-1" << endl;
      exit(0);
    }
  }
  if (S[p].first > S[p].second) swap(S[p].first, S[p].second);
  num[p] = 2;
  if (S[p].first == -1) num[p]--;
  if (S[p].second == -1) num[p]--;
}
int main() {
  scanf("%d", &n);
  for (int i = 1; i < n; i++) {
    int a, b;
    scanf("%d%d", &a, &b);
    E[a].push_back(b);
    E[b].push_back(a);
    d[a]++;
    d[b]++;
  }
  queue<int> Q;
  for (int i = 1; i <= n; i++) {
    if (E[i].size() == 1) {
      Q.push(i);
      ins(i, 0);
      vis[i] = 1;
    }
  }
  while (!Q.empty()) {
    int now = Q.front();
    vis[now] = 1;
    Q.pop();
    if (d[now] == 0) break;
    int next = 0;
    for (int i = 0; i < E[now].size(); i++) {
      int v = E[now][i];
      if (vis[v]) continue;
      next = v;
    }
    d[next]--;
    ins(next, S[now].second + 1);
    if (d[next] == 1 && num[next] == 1) {
      Q.push(next);
      vis[next] = 1;
    }
  }
  int ans = 0, num2 = 0;
  for (int i = 1; i <= n; i++) {
    if (num[i] == 0) {
      cout << "-1" << endl;
      return 0;
    }
    if (num[i] == 1) {
      ans = max(ans, S[i].second);
    }
    if (num[i] == 2) {
      ans = max(ans, S[i].first + S[i].second);
      num2++;
    }
  }
  if (num2 > 1) {
    cout << "-1" << endl;
    return 0;
  }
  if (ans == 0) {
    cout << "-1" << endl;
    return 0;
  }
  while (ans % 2 == 0) {
    ans /= 2;
  }
  cout << ans << endl;
}
