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;
vector<vector<int> > adj(212345);
int good[212345], len[212345];
int dfs(int cur, int prev) {
  set<int> seti;
  set<int>::iterator it;
  int i;
  good[cur] = 1;
  for (i = 0; i < adj[cur].size(); i++) {
    if (adj[cur][i] != prev) {
      dfs(adj[cur][i], cur);
    }
  }
  for (i = 0; i < adj[cur].size(); i++) {
    if (adj[cur][i] != prev) {
      if (!good[adj[cur][i]]) {
        good[cur] = 0;
      } else {
        if (seti.size() != 2) seti.insert(len[adj[cur][i]]);
      }
    }
  }
  int val = seti.size();
  if (good[cur] == 1) {
    if (seti.size() == 2) {
      good[cur] = 0;
      len[cur] = -1;
    } else if (seti.size() == 1) {
      len[cur] = *(seti.begin()) + 1;
    } else {
      len[cur] = 0;
    }
  } else {
    len[cur] = -1;
  }
  return 0;
}
int finded(int val) {
  while (val % 2 == 0) {
    val /= 2;
  }
  cout << val << endl;
  return 0;
}
int dfs2(int cur, int prev) {
  map<int, int> mapi;
  mapi.clear();
  map<int, int>::iterator it;
  int i, ind, flag = 0;
  for (i = 0; i < adj[cur].size(); i++) {
    if (!good[adj[cur][i]]) {
      flag++;
      ind = i;
    } else {
      mapi[len[adj[cur][i]]]++;
    }
  }
  if (mapi.size() > 2 || flag > 1) {
    cout << -1 << endl;
    exit(0);
  }
  if (flag == 0 && mapi.size() < 3) {
    int sumi = 0;
    for (it = mapi.begin(); it != mapi.end(); it++) {
      sumi += it->first;
    }
    sumi += mapi.size();
    finded(sumi);
    exit(0);
  }
  if (flag == 1 && mapi.size() == 2) {
    cout << -1 << endl;
    exit(0);
  }
  if (flag == 1) {
    int sumi = 0;
    for (it = mapi.begin(); it != mapi.end(); it++) {
      sumi += it->first;
    }
    if (mapi.size() == 1)
      len[cur] = 1 + sumi;
    else
      len[cur] = 0;
    good[cur] = 1;
    dfs2(adj[cur][ind], prev);
  }
  return 0;
}
int main() {
  std::ios::sync_with_stdio(false);
  int n, i, u, v;
  cin >> n;
  for (i = 0; i < n - 1; i++) {
    cin >> u >> v;
    u--;
    v--;
    adj[u].push_back(v);
    adj[v].push_back(u);
  }
  dfs(0, -1);
  dfs2(0, -1);
  cout << -1 << endl;
  return 0;
}
