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 long double pi = acos(-1);
const int n_ = 2e5 + 5;
int n, st, ok = 1, ans = 1e7;
vector<int> adj[n_];
set<int> ss;
int DFS(int u = st, int p = -1) {
  int ret = 0, done = 1;
  set<int> s;
  for (int i : adj[u]) {
    if (i != p) s.insert(DFS(i, u));
  }
  if (s.size() > (1 + (st == u))) ok = 0;
  if (ok && adj[u].size() > 2) ans = min(ans, (*s.rbegin()) + 1);
  if (st == u) ss = s;
  return (s.size() ? (*s.rbegin()) : 0) + 1;
}
int main() {
  scanf("%d", &n);
  for (int i = 1; i < n; i++) {
    int u, v;
    scanf("%d %d", &u, &v);
    adj[u].push_back(v);
    adj[v].push_back(u);
  }
  for (int i = 1; i <= n; i++) {
    if (adj[i].size() > 2) {
      st = i;
      break;
    }
  }
  if (n == 2) {
    puts("0");
    return 0;
  }
  if (st) DFS();
  if (!ok)
    puts("-1");
  else {
    int x;
    if (st)
      x = (*ss.begin()) + (*ss.rbegin()) + 1;
    else
      x = n;
    while ((x & 1) && x > 1) {
      ans = min(ans, x / 2);
      x = (x + 1) / 2;
    }
    printf("%d", ans);
  }
  return 0;
}
