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;
long long INF = numeric_limits<long long>::max();
unordered_map<long long, long long> dp;
long long rec(vector<vector<int>> &g, int p, int v) {
  long long key = 1000000 * p + v;
  if (dp.count(key)) {
    return dp[key];
  }
  long long r = 0;
  set<long long> s;
  for (int i = 0; i < g[v].size(); ++i) {
    if (g[v][i] == p) continue;
    long long c = rec(g, v, g[v][i]);
    if (c == INF) {
      r = INF;
      break;
    }
    s.insert(c);
    r = c + 1;
    if (s.size() > 1) {
      r = INF;
      break;
    }
  }
  assert(r >= 0);
  dp[key] = r;
  return r;
}
int main(int argc, const char *argv[]) {
  std::ios::sync_with_stdio(false);
  int n;
  cin >> n;
  vector<vector<int>> g(n);
  for (int i = 0; i < n - 1; ++i) {
    int v1, v2;
    cin >> v1 >> v2;
    --v1;
    --v2;
    g[v1].push_back(v2);
    g[v2].push_back(v1);
  }
  long long res = INF;
  for (int i = 0; i < n; ++i) {
    set<long long> s;
    bool skip = false;
    for (int j = 0; j < g[i].size(); ++j) {
      long long c = rec(g, i, g[i][j]);
      if (c == INF) {
        skip = true;
        break;
      }
      s.insert(c);
      if (s.size() > 2) {
        skip = true;
        break;
      }
    }
    if (skip) {
      continue;
    }
    long long c = -1;
    if (s.size() == 1) {
      c = *s.begin() + 1;
    } else if (s.size() == 2) {
      c = accumulate(s.begin(), s.end(), 0ll) + 2;
    }
    while (c % 2 != 1) {
      c /= 2;
    }
    res = min(res, c);
  }
  if (res == INF) {
    cout << -1 << endl;
  } else {
    cout << res << endl;
  }
  return 0;
}
