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;
int use[maxn];
bool vis[maxn];
vector<int> son[maxn];
map<int, bool> mp[maxn];
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  ;
  int n;
  cin >> n;
  for (int j = 1; j < n; ++j) {
    int u, v;
    cin >> u >> v;
    son[u].push_back(v);
    son[v].push_back(u);
  }
  queue<int> que;
  for (int j = 1; j <= n; ++j) {
    if (son[j].size() == 1) {
      mp[j][0] = 1;
      que.push(j);
    }
  }
  int ans = 0;
  bool flag = 1;
  while (!que.empty()) {
    int tis = que.front();
    que.pop();
    if (vis[tis]) continue;
    vis[tis] = 1;
    if (use[tis] == son[tis].size() - 1) {
      if (mp[tis].size() == 1) {
        int len = (mp[tis].begin())->first;
        for (int j = 0; j < son[tis].size(); ++j) {
          int nx = son[tis][j];
          if (vis[nx] == 0) {
            mp[nx][len + 1] = 1;
            ++use[nx];
            if (son[nx].size() - use[nx] <= 1) que.push(nx);
          }
        }
      } else
        flag = 0;
    } else {
      if (mp[tis].size() > 2)
        flag = 0;
      else {
        map<int, bool>::iterator it = mp[tis].begin();
        ans = 0;
        ans += (it->first);
        if (mp[tis].size() == 2) {
          ++it;
          ans += (it->first);
        }
      }
    }
  }
  while (ans > 0 && ans % 2 == 0) ans /= 2;
  if (flag)
    cout << ans << endl;
  else
    cout << "-1" << endl;
  return 0;
}
