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 N = 200010;
struct edge {
  int to, pre;
} e[N << 1];
int u[N], l = 0;
void ins(int a, int b) { e[++l] = (edge){b, u[a]}, u[a] = l; }
int f[N], g[N], b[N], father[N];
void dfs(int x, int fa) {
  father[x] = fa;
  for (int i = u[x]; i; i = e[i].pre)
    if (e[i].to != fa) dfs(e[i].to, x);
  int l = 0;
  for (int i = u[x]; i; i = e[i].pre)
    if (e[i].to != fa) b[++l] = (~f[e[i].to]) ? f[e[i].to] + 1 : -1;
  if (l) {
    sort(b + 1, b + l + 1);
    l = unique(b + 1, b + l + 1) - b - 1;
  }
  if (!l)
    f[x] = 0;
  else if (l > 1 || b[1] == -1)
    f[x] = -1;
  else
    f[x] = b[1];
}
void dp(int x, int fa) {
  bool flag = true;
  int s[2] = {0, 0}, cnt[2] = {0, 0};
  if (g[x] == -1)
    flag = false;
  else if (g[x])
    s[0] = g[x], cnt[0] = 1;
  for (int i = u[x]; i; i = e[i].pre)
    if (e[i].to != fa) {
      int t = (f[e[i].to] == -1) ? -1 : f[e[i].to] + 1;
      for (int j = 0; j <= 1; j++)
        if (!s[j] || s[j] == t) {
          s[j] = t, cnt[j]++;
          break;
        }
      if (s[0] != t && s[1] != t) flag = false;
    }
  if (!flag) {
    for (int i = u[x]; i; i = e[i].pre)
      if (e[i].to != fa) g[e[i].to] = -1, dp(e[i].to, x);
    return;
  }
  for (int i = u[x]; i; i = e[i].pre)
    if (e[i].to != fa) {
      int t = ((f[e[i].to] == -1) ? -1 : f[e[i].to] + 1), k = 0;
      for (int j = 0; j <= 1; j++)
        if (s[j] == t) {
          k = j;
          break;
        }
      if (cnt[k] > 1 || s[k ^ 1] == -1)
        g[e[i].to] = -1, dp(e[i].to, x);
      else
        g[e[i].to] = s[k ^ 1] + 1, dp(e[i].to, x);
    }
}
void upd(int &a, int b) {
  if (~b) a = (b < a || a == -1) ? b : a;
}
int main() {
  int n;
  scanf("%d", &n);
  for (int i = 1; i <= n - 1; i++) {
    int a, b;
    scanf("%d%d", &a, &b);
    ins(a, b), ins(b, a);
  }
  dfs(1, 0);
  dp(1, 0);
  int ans = -1;
  for (int x = 1; x <= n; x++) {
    int l = 0;
    if (g[x]) b[++l] = g[x];
    for (int i = u[x]; i; i = e[i].pre)
      if (e[i].to != father[x])
        b[++l] = (f[e[i].to] == -1) ? (-1) : f[e[i].to] + 1;
    sort(b + 1, b + l + 1);
    l = unique(b + 1, b + l + 1) - b - 1;
    int t = -1;
    if (b[1] == -1) continue;
    if (l == 1)
      t = b[1];
    else if (l == 2)
      t = b[1] + b[2];
    if (~t) {
      while (t % 2 == 0) t /= 2;
      upd(ans, t);
    }
  }
  cout << ans << endl;
  return 0;
}
