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;
int n, u, v, mx, st, st1, st2, tmp1, tmp2, ans;
int f[200010], lst[200010];
vector<int> p[200010];
bool flag[200010];
int Dfs(int x) {
  if (p[x].size() == 1) return f[x];
  int res = 0;
  for (int i = 0; i < p[x].size(); i++)
    if (p[x][i] != lst[x]) {
      f[p[x][i]] = f[x] + 1;
      lst[p[x][i]] = x;
      int tmp = Dfs(p[x][i]);
      if (res != 0 && tmp != res) return -1;
      res = tmp;
    }
  return res;
}
int main() {
  memset(flag, 0, sizeof(flag));
  scanf("%d", &n);
  for (int i = 1; i < n; i++) {
    scanf("%d%d", &u, &v);
    p[u].push_back(v);
    p[v].push_back(u);
  }
  f[1] = lst[1] = 0;
  Dfs(1);
  mx = -1;
  for (int i = 1; i <= n; i++)
    if (f[i] > mx) mx = f[i], st1 = i;
  f[st1] = lst[st1] = 0;
  Dfs(st1);
  mx = -1;
  for (int i = 1; i <= n; i++)
    if (f[i] > mx) mx = f[i], st2 = i;
  st = st2;
  for (int i = 0; i < mx / 2; i++) st = lst[st];
  f[st] = lst[st] = tmp1 = tmp2 = 0;
  for (int i = 0; i < p[st].size(); i++) {
    f[p[st][i]] = 1;
    lst[p[st][i]] = st;
    int tmp = Dfs(p[st][i]);
    if (tmp == -1) {
      printf("-1\n");
      return 0;
    }
    if (tmp != tmp1 && tmp != tmp2)
      if (tmp1 == 0)
        tmp1 = tmp;
      else if (tmp2 == 0)
        tmp2 = tmp;
      else {
        printf("-1\n");
        return 0;
      }
  }
  ans = tmp1 + tmp2;
  while (ans % 2 == 0) ans >>= 1;
  printf("%d\n", ans);
  return 0;
}
