#include <bits/stdc++.h>
using namespace std;
int n;
vector<int> G[200010];
int c[200010];
int bad[200100];
void dfs(int o, int fa) {
  bool tem = false;
  c[o] = -1;
  bad[o] = -1;
  for (auto &i : G[o]) {
    if (i == fa) continue;
    tem = true;
    dfs(i, o);
  }
  if (tem == false) {
    c[o] = 1;
    return;
  }
  for (auto &i : G[o]) {
    if (i == fa) continue;
    if (bad[i] != -1) {
      if (bad[o] != -1) {
        printf("-1\n");
        exit(0);
      }
      bad[o] = i;
    }
  }
  if (bad[o] != -1) return;
  int tmp = -1;
  for (auto &i : G[o]) {
    if (i == fa) continue;
    if (tmp == -1) {
      tmp = c[i];
      continue;
    }
    if (tmp != c[i]) {
      bad[o] = 0;
      return;
    }
  }
  c[o] = tmp + 1;
}
int ans;
void findB(int o) {
  if (bad[o] == 0) {
    vector<int> tt;
    for (auto &i : G[o]) {
      tt.push_back(c[i]);
    }
    sort(tt.begin(), tt.end());
    tt.resize(unique(tt.begin(), tt.end()) - tt.begin());
    if (tt.size() >= 3) {
      printf("-1\n");
      exit(0);
    }
    if (tt.size() == 1) {
      ans = tt[0];
    } else {
      ans = tt[0] + tt[1];
    }
    return;
  }
  int tmp = -1;
  for (auto &i : G[o]) {
    if (i == bad[o]) continue;
    if (tmp == -1) {
      tmp = c[i];
    }
    if (tmp != c[i]) {
      printf("-1\n");
      exit(0);
    }
  }
  if (tmp == -1) {
    c[o] = 1;
  } else {
    c[o] = tmp + 1;
  }
  findB(bad[o]);
}
int main() {
  scanf("%d", &n);
  for (int i = 1; i < n; ++i) {
    int u, v;
    scanf("%d%d", &u, &v);
    G[u].push_back(v);
    G[v].push_back(u);
  }
  dfs(1, -1);
  if (c[1] > 0) {
    c[1]--;
    while (c[1] && c[1] % 2 == 0) c[1] /= 2;
    printf("%d\n", c[1]);
    return 0;
  }
  findB(1);
  while (ans % 2 == 0) ans /= 2;
  printf("%d\n", ans);
  return 0;
}
