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 int N = 2e5 + 5;
vector<int> e[N];
set<int> s[N];
queue<int> q;
bool vis[N];
int d[N];
int main() {
  int n;
  scanf("%d", &n);
  for (int i = 1; i < n; i++) {
    int u, v;
    scanf("%d %d", &u, &v);
    d[u]++, d[v]++;
    e[u].push_back(v), e[v].push_back(u);
  }
  for (int i = 1; i <= n; i++)
    if (d[i] == 1) q.push(i), s[i].insert(0);
  while (q.size()) {
    int tp = q.front();
    q.pop();
    vis[tp] = true;
    for (int i = 0; i < e[tp].size(); i++) {
      int v = e[tp][i];
      if (vis[v]) continue;
      d[v]--;
      s[v].insert(*(s[tp].begin()) + 1);
      if (d[v] == 1 && s[v].size() == 1) q.push(v);
    }
  }
  int cnt = 0, ans = 0;
  for (int i = 1; i <= n; i++)
    if (s[i].size() > 2 || s[i].size() == 0)
      return 0 * puts("-1");
    else if (s[i].size() == 1)
      ans = max(ans, *s[i].begin());
    else
      cnt++, ans = max(ans, (*s[i].begin()) + (*s[i].rbegin()));
  if (cnt > 1)
    puts("-1");
  else {
    while (ans % 2 == 0) ans /= 2;
    printf("%d\n", ans);
  }
  return 0;
}
