#include <bits/stdc++.h>
#pragma comment(linker, "/STACK:100000000")
using namespace std;
const int N = 200100;
vector<int> m[N], v[N];
queue<int> q;
int h[N], u[N];
int main() {
  int n, i, j, k;
  scanf("%d", &n);
  for (k = n - 1; k--;
       scanf("%d%d", &i, &j), i--, j--, m[i].push_back(j), m[j].push_back(i))
    ;
  for (i = 0; i < n; i++) {
    h[i] = m[i].size();
    if (h[i] == 1) {
      q.push(i);
      v[i].push_back(0);
    }
  }
  for (; !q.empty();) {
    i = q.front();
    q.pop();
    k = v[i][0];
    u[i] = 1;
    if (h[i] > 0) {
      bool ok = 1;
      for (int j : v[i])
        if (j != k) ok = 0;
      if (!ok) break;
    }
    for (int j : m[i])
      if (!u[j]) {
        h[j]--;
        v[j].push_back(k + 1);
        if (h[j] == 1) q.push(j);
      }
  }
  if (h[i] > 0)
    printf("-1\n");
  else {
    sort(v[i].begin(), v[i].end());
    v[i].resize(unique(v[i].begin(), v[i].end()) - v[i].begin());
    if (v[i].size() > 2)
      printf("-1\n");
    else {
      k = 0;
      for (int j : v[i]) k += j;
      for (; k % 2 == 0; k /= 2)
        ;
      printf("%d\n", k);
    }
  }
  return 0;
}
