10
4 2
7 4
2 6
2 5
4 8
10 3
2 9
9 1
5 10
 10
5 10
7 8
8 3
2 6
3 2
9 7
4 5
10 1
6 4
 4
4 1
4 3
4 2
 3
3 1
1 2
 9
1 2
1 3
1 4
1 5
1 6
6 7
6 8
8 9
 5
1 5
2 3
2 4
1 2
 8
6 1
4 7
4 8
8 5
7 6
4 3
4 2
 7
5 6
5 7
5 1
7 4
6 3
3 2
 3
1 3
3 2
 2
1 2
 5
5 4
4 3
3 1
5 2
 6
1 6
3 1
6 4
5 3
2 5
 11
8 9
2 7
1 11
3 2
9 1
8 5
8 6
5 4
4 10
8 3
 11
11 9
6 7
7 1
8 11
5 6
3 5
9 3
10 8
2 4
4 10
 12
12 6
6 7
8 11
4 8
10 4
12 3
2 10
6 2
12 9
4 1
9 5

-1
 9
 1
 1
 3
 3
 -1
 -1
 1
 1
 1
 5
 1
 5
 -1

#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;
}
