#include <bits/stdc++.h>
using namespace std;
const int INF = 0x3f3f3f3f;
const double PI = acos(-1.0);
void no() {
  cout << -1 << endl;
  exit(0);
}
void yes(int x) {
  while (!(x % 2)) x /= 2;
  cout << x << endl;
  exit(0);
}
const int N = 2e5 + 5;
int n;
set<int> g[N];
int chega[N][2];
bool diff(int at, int sz) {
  if (!chega[at][0] or !chega[at][1]) return 0;
  if (chega[at][0] == sz) return 0;
  if (chega[at][1] == sz) return 0;
  return 1;
}
bool add(int at, int sz) {
  if (chega[at][0] == sz or chega[at][1] == sz) return 1;
  if (!chega[at][0])
    chega[at][0] = sz;
  else
    chega[at][1] = sz;
  return 0;
}
void go(int at, int sz) {
  if (diff(at, sz)) {
    no();
  }
  if (g[at].size() == 0) {
    add(at, sz);
    int extra = 0;
    if (chega[at][0] and chega[at][1]) extra = 1;
    yes(chega[at][0] + chega[at][1] - extra - 1);
  }
  int neig = g[at].size();
  if (chega[at][0]) neig++;
  if (chega[at][1]) neig++;
  if (neig - add(at, sz) > 1) {
    return;
  }
  int next = *(g[at].begin());
  g[at].erase(next);
  g[next].erase(at);
  go(next, sz + 1);
}
int main(void) {
  ios_base::sync_with_stdio(false);
  cin >> n;
  for (int i = 1; i < n; i++) {
    int a, b;
    cin >> a >> b;
    g[a].insert(b);
    g[b].insert(a);
  }
  for (int i = 1; i <= n; i++)
    if (g[i].size() == 1 and !chega[i][0] and !chega[i][1]) go(i, 1);
  no();
  return 0;
}
