#include <bits/stdc++.h>
using namespace std;
int n;
vector<vector<int> > g;
vector<int> sz;
const int INF = 1e9;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0), cout.tie(0);
  cin >> n;
  g.resize(n);
  sz.resize(n);
  for (int i = 0; i < n - 1; i++) {
    int a, b;
    cin >> a >> b;
    g[a - 1].push_back(b - 1);
    g[b - 1].push_back(a - 1);
  }
  queue<int> q;
  vector<int> d(n, INF);
  vector<int> sec(n, INF);
  vector<int> p(n);
  for (int i = 0; i < n; i++) {
    sz[i] = g[i].size();
    if (sz[i] == 1) {
      q.push(i);
      d[i] = 0;
    }
  }
  while (!q.empty()) {
    int v = q.front();
    q.pop();
    for (int i : g[v]) {
      if (sz[i] != 0) {
        if (d[i] == INF) {
          d[i] = d[v] + 1;
          sz[i]--;
          if (sz[i] == 1) {
            q.push(i);
          }
        } else {
          if (d[i] == d[v] + 1) {
            sz[i]--;
            if (sz[i] == 1) {
              q.push(i);
            }
          } else {
            if (sec[i] == INF) {
              sec[i] = d[v] + 1;
            } else {
              if (sec[i] != d[v] + 1) {
                cout << -1;
                return 0;
              }
            }
          }
        }
      }
    }
    sz[v] = 0;
  }
  int numb = -1;
  for (int i = 0; i < n; i++) {
    if (sec[i] != INF) {
      if (numb != -1) {
        cout << -1;
        return 0;
      }
      numb = i;
    }
  }
  int ans = 0;
  if (numb != -1)
    ans = d[numb] + sec[numb];
  else {
    for (int i = 0; i < n; i++) ans = max(ans, d[i]);
  }
  while (ans % 2 == 0) ans /= 2;
  cout << ans;
  return 0;
}
