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 + 50;
vector<int> e[MAXN];
int path[MAXN];
int nroot;
void DFS(int x, int p) {
  (void)0;
  vector<int> tmp;
  for (int t : e[x]) {
    if (t == p) continue;
    DFS(t, x);
    (void)0;
    tmp.push_back(path[t]);
  }
  if (((int)(tmp).size()) == 0) {
    (void)0;
    path[x] = 1;
    return;
  }
  sort((tmp).begin(), (tmp).end());
  if (tmp[0] < 0) {
    path[x] = -1;
    return;
  }
  if (p != 0) {
    for (int i = 1; i < ((int)(tmp).size()); i++) {
      if (tmp[i] != tmp[i - 1]) {
        nroot = x;
        path[x] = -1;
        return;
      }
    }
    path[x] = tmp[0] + 1;
    return;
  }
  tmp.resize(unique((tmp).begin(), (tmp).end()) - begin(tmp));
  if (((int)(tmp).size()) > 2)
    path[x] = -1;
  else if (((int)(tmp).size()) == 2)
    path[x] = tmp[0] + tmp[1];
  else
    path[x] = tmp[0];
}
int main() {
  int n;
  scanf("%d", &n);
  for (int i = 1; i < n; i++) {
    int a, b;
    scanf("%d%d", &a, &b);
    e[a].push_back(b);
    e[b].push_back(a);
  }
  int root = 0;
  for (int i = 1; i <= n; i++)
    if (((int)(e[i]).size()) >= 3) {
      root = i;
      break;
    }
  int ans;
  if (root == 0)
    ans = n - 1;
  else {
    nroot = root;
    DFS(root, 0);
    if (path[root] < 0) {
      (void)0;
      root = nroot;
      DFS(root, 0);
    }
    ans = path[root];
  }
  while (ans % 2 == 0) ans /= 2;
  printf("%d\n", ans);
  return 0;
}
