#include <bits/stdc++.h>
using namespace std;
const long long maxn = 2e5 + 1, mod = 1e9 + 7;
vector<int> g[maxn];
int dfs(int cur, int par, int h) {
  map<int, int> mapp;
  for (auto it : g[cur]) {
    if (it == par) continue;
    mapp[dfs(it, cur, h + 1)];
  }
  if (mapp.size() > 2) {
    cout << -1;
    exit(0);
  } else if (mapp.size() == 2) {
    if (mapp.find(h) == mapp.end()) {
      cout << -1;
      exit(0);
    } else {
      for (auto it : mapp) {
        if (it.first != h) return it.first + 1;
      }
    }
  } else {
    if (mapp.size() == 0) {
      return 1;
    } else {
      for (auto it : mapp) {
        return it.first + 1;
      }
    }
  }
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  int n;
  cin >> n;
  for (long long i = 0; i < n - 1; i++) {
    int u, v;
    cin >> u >> v;
    g[u].push_back(v);
    g[v].push_back(u);
  }
  int root;
  for (long long i = 0; i < n + 1; i++) {
    if (i == 0) continue;
    if (g[i].size() == 1) {
      root = i;
      break;
    }
  }
  int ans = dfs(root, root, 0);
  ans -= 1;
  while (ans % 2 == 0) ans /= 2;
  cout << ans;
  return 0;
}
