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 = 200001;
int n, root;
struct Edge {
  int to, next;
} edge[N << 1];
int head[N], cnt;
void add_edge(int u, int v) {
  cnt++;
  edge[cnt].to = v;
  edge[cnt].next = head[u];
  head[u] = cnt;
  return;
}
int dfs(int u, int father) {
  set<int> S;
  for (int i = head[u]; i; i = edge[i].next) {
    int v = edge[i].to;
    if (v == father) continue;
    int res = dfs(v, u);
    if (res == -1) return -1;
    S.insert(res + 1);
  }
  if (S.size() > 2)
    return -1;
  else if (S.empty())
    return 0;
  if (S.size() == 1)
    return *S.begin();
  else if (S.size() == 2 && father == 0)
    return *S.rbegin() + *S.begin();
  else
    root = u;
  return -1;
}
int main() {
  scanf("%d", &n);
  for (int i = 1; i < n; i++) {
    int x, y;
    scanf("%d%d", &x, &y);
    add_edge(x, y);
    add_edge(y, x);
  }
  int res = dfs(1, 0);
  if (res == -1 && root) res = dfs(root, 0);
  printf("%d", res / (res & -res));
  return 0;
}
