#include <bits/stdc++.h>
using namespace std;
void insert(vector<set<int> > &adj, map<pair<int, int>, int> &mp,
            vector<int> &branch, vector<int> &tail, int leaf, int cnt) {
  int b = branch[leaf];
  pair<int, int> p = make_pair(cnt, b);
  if (mp.count(p)) {
    adj[b].erase(tail[leaf]);
    if (adj[b].size() == 1) {
      return;
    } else if (adj[b].size() == 2) {
      leaf = mp[p];
      mp.erase(p);
      int last = tail[leaf];
      int u = b;
      while (adj[u].size() == 2) {
        int v1 = *adj[u].begin();
        int v2 = *(++adj[u].begin());
        if (v1 == last) {
          last = u;
          u = v2;
        } else {
          last = u;
          u = v1;
        }
        cnt++;
      }
      if (adj[u].size() == 1) {
        mp.clear();
        mp[make_pair(cnt, adj.size())] = leaf;
        return;
      } else {
        branch[leaf] = u;
        tail[leaf] = last;
        insert(adj, mp, branch, tail, leaf, cnt);
      }
    } else {
    }
  } else {
    mp[p] = leaf;
  }
}
int main(int argc, char **argv) {
  int n;
  scanf("%d", &n);
  vector<set<int> > adj(n);
  for (int i = 0; i < n - 1; i++) {
    int u, v;
    scanf("%d%d", &u, &v);
    u--;
    v--;
    adj[u].insert(v);
    adj[v].insert(u);
  }
  vector<int> branch(n, -1);
  vector<int> tail(n, -1);
  map<pair<int, int>, int> mp;
  for (int u = 0; u < n; u++) {
    if (adj[u].size() == 1) {
      int leaf = u;
      int cnt = 1;
      int last = leaf;
      int v = *adj[last].begin();
      while (adj[v].size() == 2) {
        int v1 = *adj[v].begin();
        int v2 = *(++adj[v].begin());
        if (v1 == last) {
          last = v;
          v = v2;
        } else if (v2 == last) {
          last = v;
          v = v1;
        } else {
          abort();
        }
        cnt++;
      }
      if (adj[v].size() == 1) {
        mp.clear();
        mp[make_pair(cnt, n)] = leaf;
        break;
      } else {
        branch[leaf] = v;
        tail[leaf] = last;
        insert(adj, mp, branch, tail, leaf, cnt);
      }
    }
  }
  if (mp.size() == 1) {
    int cnt = mp.begin()->first.first;
    while (cnt % 2 == 0) {
      cnt /= 2;
    }
    printf("%d\n", cnt);
  } else {
    puts("-1");
  }
  return 0;
}
