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;
#pragma comment(linker, "/STACK:102400000,102400000")
long long mul(long long a, long long b) { return (a * b) % (1000000007); }
long long add(long long a, long long b) { return (a + b) % (1000000007); }
long long sub(long long a, long long b) {
  return ((a - b) % (1000000007) + (1000000007)) % (1000000007);
}
void upd(long long &a, long long b) {
  a = (a % (1000000007) + b % (1000000007)) % (1000000007);
}
int read() {
  int x = 0, f = 1;
  char ch = getchar();
  while (!isdigit(ch)) {
    if (ch == '-') f = -1;
    ch = getchar();
  }
  while (isdigit(ch)) {
    x = x * 10 + ch - '0';
    ch = getchar();
  }
  return x * f;
}
vector<int> edges[(212345)];
int ind[(212345)];
queue<int> q;
vector<int> le[(212345)];
bool check(int i) {
  int sz = ((le[i]).size());
  if (!sz) return 1;
  sort((le[i]).begin(), (le[i]).end());
  if (le[i][0] == le[i][sz - 1]) return 1;
  return 0;
}
bool vis[(212345)] = {0};
int main() {
  int n = read();
  for (int i = 1; i <= n - 1; i++) {
    int u = read(), v = read();
    edges[u].push_back(v);
    edges[v].push_back(u);
    ind[u]++, ind[v]++;
  }
  for (int i = 1; i <= n; i++)
    if (ind[i] == 1) {
      q.push(i);
    }
  for (int i = 1; i <= n - 1; i++)
    if (q.size() >= 1) {
      int now = q.front();
      vis[now] = 1;
      q.pop();
      int sz = edges[now].size();
      for (int i = 0; i < sz; i++) {
        int v = edges[now][i];
        if (ind[v]) {
          sort((le[now]).begin(), (le[now]).end());
          int len = ((le[now]).size());
          int p = 1;
          if (!len) {
            le[v].push_back(1);
          } else if (le[now][len - 1] != le[now][0]) {
          } else {
            le[v].push_back(le[now][0] + 1);
          }
          ind[now]--, ind[v]--;
          if (ind[v] == 1) {
            if (check(v)) q.push(v);
          }
        }
      }
    }
  vector<int> not_vis;
  for (int i = 1; i <= n; i++)
    if (!vis[i]) {
      not_vis.push_back(i);
    }
  if (((not_vis).size()) > 1) {
    puts("-1");
    return 0;
  }
  int p = not_vis[0];
  sort((le[p]).begin(), (le[p]).end());
  vector<int>::iterator iter = unique(le[p].begin(), le[p].end());
  le[p].erase(iter, le[p].end());
  if (((le[p]).size()) > 2) {
    puts("-1");
    return 0;
  }
  int len = le[p][0];
  if (((le[p]).size()) == 2) len += le[p][1];
  while (len % 2 == 0) len /= 2;
  cout << len << endl;
  return 0;
}
