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, st2, f[200010], lst[200010];
vector<int> p[200010];
bool flag[200010];
void Dfs(int x, int _last, int d, bool q) {
  f[x] = d;
  if (q && !flag[_last])
    lst[x] = lst[_last];
  else
    lst[x] = _last;
  for (int i = 0; i < p[x].size(); i++)
    if (p[x][i] != _last) Dfs(p[x][i], x, d + 1, q);
}
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);
  }
  Dfs(1, 0, 0, 0);
  mx = -1;
  for (int i = 1; i <= n; i++)
    if (f[i] > mx) {
      mx = f[i];
      st = i;
    }
  Dfs(st, 0, 0, 0);
  mx = -1;
  for (int i = 1; i <= n; i++)
    if (f[i] > mx) {
      mx = f[i];
      st2 = i;
    }
  int tmp = st2;
  while (tmp != st) {
    flag[tmp] = 1;
    tmp = lst[tmp];
  }
  flag[st] = 1;
  Dfs(st, 0, 0, 1);
  if (mx & 1) {
    for (int i = 1; i <= n; i++)
      if (i != st && p[i].size() == 1 &&
          !(f[i] == mx || f[i] == 2 * f[lst[i]])) {
        printf("-1\n");
        return 0;
      }
    printf("%d\n", mx);
  } else {
    int tmp = -1;
    for (int i = 1; i <= n; i++)
      if (i != st && p[i].size() == 1 &&
          !(f[i] == mx || f[i] == 2 * f[lst[i]])) {
        if (f[lst[i]] == mx / 2) {
          if (tmp == -1 || tmp == f[i] - mx / 2)
            tmp = f[i] - mx / 2;
          else {
            printf("-1\n");
            return 0;
          }
        } else {
          printf("-1\n");
          return 0;
        }
      }
    if (tmp != -1)
      for (int i = 1; i <= n; i++)
        if (i != st && p[i].size() == 1 &&
            !((f[i] == mx && f[lst[i]] > mx / 2) ||
              (f[i] == 2 * f[lst[i]] && f[lst[i]] < mx / 2))) {
          printf("-1\n");
          return 0;
        }
    if (tmp != -1) mx = mx / 2 + tmp;
    while (mx % 2 == 0) mx >>= 1;
    printf("%d\n", mx);
  }
  return 0;
}
