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 maxn = 2e5 + 10;
vector<int> g[maxn];
int par[maxn];
int p[maxn];
void dfs(int v, int pp = 0) {
  p[v] = p[pp] + 1;
  par[v] = pp;
  for (int x : g[v]) {
    if (x != pp) dfs(x, v);
  }
}
int main() {
  p[0] = -1;
  int n;
  cin >> n;
  int cnt1 = 0, cnt2 = 0;
  for (int i = 1; i < n; i++) {
    int a, b;
    cin >> a >> b;
    g[a].push_back(b);
    g[b].push_back(a);
  }
  dfs(1);
  int root = 0;
  for (int i = 1; i <= n; i++)
    if (p[i] > p[root]) root = i;
  fill(p, p + n + 1, 0);
  fill(par, par + n + 1, 0);
  p[0] = -1;
  dfs(root);
  int d = -1;
  root = 0;
  for (int i = 1; i <= n; i++) {
    if (p[i] > p[root]) root = i, d = p[i];
  }
  int h = d / 2;
  while (h--) root = par[root];
  fill(p, p + n + 1, 0);
  p[0] = -1;
  dfs(root);
  int l1 = -1;
  int l2 = -1;
  for (int i = 1; i <= n; i++) {
    if (g[i].size() == 1 and l1 == -1)
      l1 = p[i];
    else if (g[i].size() == 1 and l2 == -1 and p[i] != l1)
      l2 = p[i];
  }
  if (l2 == -1) l2 = l1;
  for (int i = 1; i <= n; i++) {
    if (g[i].size() == 1 and p[i] != l1 and p[i] != l2) {
      cout << -1 << endl;
      return 0;
    }
  }
  int ans = l1 + l2;
  while (ans % 2 == 0) ans /= 2;
  cout << ans << endl;
  return 0;
}
