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 M = 2e5 + 10;
int n, k, d, dv, mx, cent;
bool mark[M];
vector<int> g[M], lst;
void door(int v, int dr, int f) {
  mark[v] = true;
  lst.push_back(v);
  for (int i = 0; i < g[v].size(); i++)
    if (!mark[g[v][i]]) door(g[v][i], dr + 1, f);
  if (mx < dr) dv = v, mx = dr;
  if (v == f) cent = lst[lst.size() / 2];
  mark[v] = false;
  lst.pop_back();
}
int dfs(int v, int r) {
  mark[v] = true;
  set<int> neg;
  for (int i = 0; i < g[v].size(); i++)
    if (!mark[g[v][i]]) neg.insert(dfs(g[v][i], r));
  if (neg.size() == 0) return 1;
  if (*neg.begin() == -1) return -1;
  if (neg.size() == 2 && v == r) return *neg.begin() + *neg.rbegin();
  if (neg.size() > 1) return -1;
  if (v == r) return *neg.begin();
  return *neg.begin() + 1;
}
int main() {
  cin >> n;
  for (int i = 1; i < n; i++) {
    int u, v;
    scanf("%d%d", &v, &u);
    g[u].push_back(v);
    g[v].push_back(u);
  }
  door(1, 0, 0);
  mx = 0;
  int f = dv;
  door(dv, 0, 0);
  door(dv, 0, f);
  k = dfs(cent, cent);
  while (k % 2 == 0) k /= 2;
  cout << k << endl;
  return 0;
}
