#include <bits/stdc++.h>
using namespace std;
const int N = 2e5 + 5;
vector<int> e[N];
set<int> s[N];
queue<int> q;
bool vis[N];
int d[N];
int main() {
  int n;
  scanf("%d", &n);
  for (int i = 1; i < n; i++) {
    int u, v;
    scanf("%d %d", &u, &v);
    d[u]++, d[v]++;
    e[u].push_back(v), e[v].push_back(u);
  }
  for (int i = 1; i <= n; i++)
    if (d[i] == 1) q.push(i), s[i].insert(0);
  while (q.size()) {
    int tp = q.front();
    q.pop();
    vis[tp] = true;
    for (int i = 0; i < e[tp].size(); i++) {
      int v = e[tp][i];
      if (vis[v]) continue;
      d[v]--;
      s[v].insert(*(s[tp].begin()) + 1);
      if (d[v] == 1 && s[v].size() == 1) q.push(v);
    }
  }
  int cnt = 0, ans = 0;
  for (int i = 1; i <= n; i++)
    if (s[i].size() > 2 || s[i].size() == 0)
      return 0 * puts("-1");
    else if (s[i].size() == 1)
      ans = max(ans, *s[i].begin());
    else
      cnt++, ans = max(ans, (*s[i].begin()) + (*s[i].rbegin()));
  if (cnt > 1)
    puts("-1");
  else {
    while (ans % 2 == 0) ans /= 2;
    printf("%d\n", ans);
  }
  return 0;
}
