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;
const double eps = 1e-8;
template <typename T, typename S>
inline bool REMIN(T &a, const S &b) {
  return a > b ? a = b, 1 : 0;
}
template <typename T, typename S>
inline bool REMAX(T &a, const S &b) {
  return a < b ? a = b, 1 : 0;
}
int toint(const string &s) {
  stringstream ss;
  ss << s;
  int x;
  ss >> x;
  return x;
}
string tostring(int number) {
  stringstream ss;
  ss << number;
  return ss.str();
}
int bit(long long x, int pos) { return ((1ll << pos) & x) ? 1 : 0; }
void split(vector<string> &v, string t) {
  stringstream s;
  s << t;
  while (s >> t) v.push_back(t);
}
const int INF = 1e9;
const int NMAX = 1e5 + 2;
const long long MOD = 1000000007;
const long double PI = 2 * acos(0);
int T, N, M;
int a, b;
string s;
void nope(int dec = 0) {
  if (!dec)
    cout << "-1";
  else
    cout << "YES";
  exit(0);
}
set<int> eds[NMAX * 2];
int root;
int far;
set<int> pts;
void hat(int curr, int par) {
  for (int v : eds[curr]) {
    if (v != par) hat(v, curr);
  }
  pts.erase(curr);
}
int dfs(int curr, int par, int dis = 0) {
  if (par == -1) root = 0, far = -1;
  set<int> cnnode;
  vector<int> eras;
  int len = 0;
  bool flag = 0;
  for (int v : eds[curr]) {
    if (v != par) {
      len = dfs(v, curr, dis + 1);
      if (len == -1) flag = 1;
      if (((cnnode).find((len)) != (cnnode).end())) {
        eras.push_back(v);
      } else
        cnnode.insert(len);
    }
  }
  for (int e : eras) {
    eds[curr].erase(e);
    hat(e, curr);
  }
  if (((int)(eds[curr].size())) > 2 || flag) {
    if (REMAX(far, dis)) {
      root = curr;
    }
    return -1;
  }
  return len + 1;
}
int dfsl(int curr, int par) {
  int le = 0;
  for (int v : eds[curr]) {
    if (v != par) {
      le += 1 + dfsl(v, curr);
    }
  }
  return le;
}
int ma, mai;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cin >> N;
  if (N == 2) {
    cout << 1;
    return 0;
  }
  for (int(i) = int(1); (i) <= int(N); ++(i)) pts.insert(i);
  for (int(i) = int(1); (i) <= int(N - 1); ++(i)) {
    cin >> a >> b;
    eds[a].insert(b);
    eds[b].insert(a);
  }
  int dec = dfs(1, -1);
  for (int(i) = int(1); (i) <= int(3); ++(i)) {
    if (dec != -1) break;
    root = max(root, *pts.begin());
    dec = dfs(root, -1);
  }
  if (dec == -1) nope();
  int lenf = dfsl(*(pts.begin()), -1);
  while (!(lenf & 1) && lenf) lenf >>= 1;
  cout << lenf;
  return 0;
}
