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;
void ga(int N, int *A) {
  for (int i(0); i < N; i++) scanf("%d", A + i);
}
set<int> g[(1 << 18)], D[(1 << 18)];
int N, a, b, Q[(1 << 18)], e;
int pus(int a) { return a & 1 ? a : pus(a / 2); }
int main(void) {
  scanf("%d", &N);
  for (int i(0); i < N - 1; i++)
    scanf("%d%d", &a, &b), g[--a].insert(--b), g[b].insert(a);
  for (int i(0); i < N; i++)
    if (g[i].size() == 1u) Q[e++] = i;
  for (int i(0); i < e; i++) {
    if (i + 1 == N) {
      if (D[Q[i]].size() == 2u)
        printf("%d\n", pus(*D[Q[i]].begin() + *--D[Q[i]].end())), exit(0);
      printf("%d\n", pus(*D[Q[i]].begin())), exit(0);
    }
    a = D[Q[i]].empty() ? 1 : 1 + *D[Q[i]].begin();
    for (auto &h : g[Q[i]]) {
      g[h].erase(Q[i]), D[h].insert(a);
      if (g[h].size() < 2u &&
          (D[h].size() == 1u || (D[h].size() == 2u && e + 1 == N)))
        Q[e++] = h;
    }
  }
  printf("%d\n", -1), exit(0);
  ;
  return 0;
}
