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;
template <int N, int M>
struct Graph {
  int top;
  struct Vertex {
    int head;
  } V[N];
  struct Edge {
    int v, next;
  } E[M];
  void init() {
    memset(V, -1, sizeof(V));
    top = 0;
  }
  void add_edge(int u, int v) {
    E[top].v = v;
    E[top].next = V[u].head;
    V[u].head = top++;
  }
};
const int N = 2 * 100000;
int n, ans[N + 10], sum[N + 10];
Graph<N + 10, N * 2 + 10> g;
void dfs(int cur, int father) {
  sum[cur] = 1;
  for (int i = g.V[cur].head; i != -1; i = g.E[i].next) {
    int son = g.E[i].v;
    if (son == father) continue;
    dfs(son, cur);
    sum[cur] += sum[son];
    ans[cur] = max(ans[cur], sum[son]);
  }
  ans[cur] = max(ans[cur], n - sum[cur]);
}
int main() {
  while (~scanf("%d", &n)) {
    g.init();
    for (int i = 1; i < n; i++) {
      int a, b;
      scanf("%d %d", &a, &b);
      g.add_edge(a, b);
      g.add_edge(b, a);
      sum[i] = 0;
      ans[i] = 0;
    }
    sum[n] = 0;
    ans[n] = 0;
    dfs(1, 0);
    int as = 0, ok = 1;
    for (int i = 1; i <= n; i++) {
      if (ans[i] <= n / 2) {
        as = i;
        break;
      }
    }
    if (!ok || !as)
      printf("-1\n");
    else {
      memset(sum, 0, sizeof(sum));
      memset(ans, 0, sizeof(ans));
      dfs(as, 0);
      set<int> s;
      for (int i = g.V[as].head; i != -1; i = g.E[i].next) {
        int son = g.E[i].v;
        s.insert(sum[son]);
      }
      if (s.size() > 2)
        printf("-1\n");
      else {
        int ass = 0;
        for (set<int>::iterator it = s.begin(); it != s.end(); it++)
          ass += (*it);
        while (ass % 2 == 0) ass /= 2;
        printf("%d\n", ass);
      }
    }
  }
}
