#include <bits/stdc++.h>
using namespace std;
const int MAXN = 210000;
int was[MAXN];
vector<int> vv;
int us;
int n;
vector<int> eds[MAXN];
int dfs1(int v) {
  was[v] = 1;
  set<int> ss;
  int fl = 0;
  int xx = 0;
  for (int u : eds[v]) {
    if (was[u]) continue;
    int x = dfs1(u);
    if (x > 0)
      ss.insert(x);
    else
      fl = 1, xx = x;
  }
  if (ss.size() + fl >= 3) {
    cout << -1 << "\n";
    exit(0);
  }
  if (fl == 0) {
    if (ss.size() == 0) return 1;
    if (ss.size() == 1) return *ss.begin() + 1;
    if (us != -1) {
      cout << -1 << "\n";
      exit(0);
    }
    us = 1;
    vv.push_back(*ss.begin());
    vv.push_back(*ss.rbegin());
    return -1;
  }
  if (ss.empty()) {
    return xx - 1;
  }
  int x = *ss.begin();
  vv.push_back(-xx);
  vv.push_back(x);
  return -1;
}
int main() {
  scanf("%d", &n);
  for (int i = 0; i < n - 1; ++i) {
    int a, b;
    scanf("%d%d", &a, &b);
    --a, --b;
    eds[a].push_back(b);
    eds[b].push_back(a);
  }
  us = -1;
  int x = dfs1(0);
  if (x > 0) {
    --x;
    while (x % 2 == 0) x /= 2;
    cout << x << "\n";
    return 0;
  }
  int now = 0;
  if (x != -1) now = -x - 1;
  while (vv.size() > 3) {
    if (now == 0) {
      now = vv.back();
      vv.pop_back();
      now += vv.back();
      vv.pop_back();
      continue;
    }
    if (now != vv.back()) {
      cout << -1 << "\n";
      return 0;
    }
    vv.pop_back();
    now += vv.back();
    vv.pop_back();
  }
  if (now == 0) {
    now = vv[0] + vv[1];
    while (now % 2 == 0) now /= 2;
    cout << now << "\n";
    return 0;
  }
  if (now != vv[0] && now != vv[1]) {
    cout << -1 << "\n";
    return 0;
  }
  now = vv[0] + vv[1];
  while (now % 2 == 0) now /= 2;
  cout << now << "\n";
  return 0;
}
