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 = 200005;
int n, u, v, root;
vector<int> vec[maxn], v1;
int dfs(int u, int fa) {
  if (vec[u].size() == 1) return 0;
  set<int> st;
  int t;
  for (unsigned int i = 0; i < vec[u].size(); ++i) {
    int v = vec[u][i];
    if (v == fa) continue;
    t = dfs(v, u);
    st.insert(t);
  }
  if (st.size() == 1) return 1 + t;
  set<int>::iterator it;
  if (st.size() > 2) {
    puts("-1");
    exit(0);
  }
  int ret = 2;
  for (it = st.begin(); it != st.end(); ++it) ret += *it;
  if (u != root) {
    v1.push_back(u);
    if (v1.size() >= 2) {
      puts("-1");
      exit(0);
    }
  }
  return ret;
}
int main() {
  scanf("%d", &n);
  for (int i = 0; i < n - 1; ++i) {
    scanf("%d%d", &u, &v);
    vec[u].push_back(v);
    vec[v].push_back(u);
  }
  while (root <= n && vec[++root].size() <= 2) {
  }
  if (root == n + 1) {
    int len = n - 1;
    while (len > 0 && len % 2 == 0) len /= 2;
    printf("%d\n", len);
  } else {
    int len = dfs(root, -1);
    if (v1.size() > 0) len = dfs(v1[0], -1);
    while (len > 0 && len % 2 == 0) len /= 2;
    printf("%d\n", len);
  }
  return 0;
}
