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 = 200005;
vector<int> g[N];
int vis[N], n;
int Q[N], d[N], fa[N];
int bfs(int s) {
  int qn = 0;
  Q[qn++] = s;
  d[s] = 0;
  for (int i = 0; i < qn; i++) {
    int u = Q[i];
    for (int j = 0; j < g[u].size(); j++) {
      int v = g[u][j];
      if (vis[v] || d[v] != -1) continue;
      d[v] = d[u] + 1;
      fa[v] = u;
      Q[qn++] = v;
    }
  }
  int ans = Q[0];
  for (int i = 0; i < qn; i++)
    if (d[ans] < d[Q[i]]) ans = Q[i];
  for (int i = 0; i < qn; i++) d[Q[i]] = -1;
  return ans;
}
void getp(int u, vector<int> &p) {
  int s = bfs(u);
  int t = bfs(s);
  while (t != s) {
    p.push_back(t);
    t = fa[t];
  }
  p.push_back(s);
}
int gao(int u) {
  vector<int> p;
  getp(u, p);
  int pn = p.size();
  for (int i = 0; i < pn; i++) vis[p[i]] = 1;
  int f = -1;
  for (int i = 0; i < pn; i++) {
    int len = i < pn / 2 ? i : pn - i - 1;
    int u = p[i];
    for (int j = 0; j < g[u].size(); j++) {
      int v = g[u][j];
      if (vis[v]) continue;
      int tmp = gao(v);
      if (tmp == -1) return -1;
      if (tmp != len) {
        if (f != -1) return -1;
        f = tmp;
      }
    }
  }
  if (f != -1) {
    if (pn % 2) return pn / 2 + 1 + f;
    return -1;
  }
  return pn;
}
int main() {
  scanf("%d", &n);
  for (int i = 1; i < n; i++) {
    int u, v;
    scanf("%d%d", &u, &v);
    g[u].push_back(v);
    g[v].push_back(u);
  }
  memset(d, -1, sizeof(d));
  int tmp = gao(1);
  if (tmp == -1)
    printf("-1\n");
  else {
    while (tmp % 2) tmp = (tmp + 1) / 2;
    printf("%d\n", tmp - 1);
  }
  return 0;
}
