#include <bits/stdc++.h>
using namespace std;
int n, D[201000], first = 0;
vector<int> E[201000];
void DFS(int a, int pp) {
  int i;
  vector<int> TP;
  for (i = 0; i < E[a].size(); i++) {
    if (E[a][i] == pp) continue;
    DFS(E[a][i], a);
    if (D[E[a][i]] == -1) {
      D[a] = -1;
      return;
    }
    TP.push_back(D[E[a][i]] + 1);
  }
  if (TP.empty()) {
    D[a] = 0;
    return;
  }
  sort(TP.begin(), TP.end());
  int ck = 0;
  for (i = 0; i < TP.size() - 1; i++) {
    if (TP[i] != TP[i + 1]) {
      ck++;
    }
  }
  if (pp != 0) {
    if (ck) {
      D[a] = -1;
      first = a;
      return;
    }
    D[a] = TP[0];
  }
  if (pp == 0) {
    if (ck > 1) {
      D[a] = -1;
      first = a;
      return;
    }
    if (ck == 1) {
      D[a] = TP[0] + TP[TP.size() - 1];
    } else
      D[a] = TP[0];
  }
}
int main() {
  int i, a, b, g = 0;
  scanf("%d", &n);
  for (i = 1; i < n; i++) {
    scanf("%d%d", &a, &b);
    E[a].push_back(b);
    E[b].push_back(a);
  }
  a = -1;
  for (i = 1; i <= n; i++) {
    if (E[i].size() >= 3) a = i;
  }
  if (a == -1) {
    a = n - 1;
    while (a % 2 == 0) a /= 2;
    printf("%d\n", a);
    return 0;
  }
  DFS(a, 0);
  if (D[a] != -1) {
    g = D[a];
  } else {
    DFS(first, 0);
    if (D[first] == -1) {
      printf("-1\n");
      return 0;
    }
    g = D[first];
  }
  while (g % 2 == 0) g /= 2;
  printf("%d\n", g);
}
