#include <bits/stdc++.h>
using namespace std;
vector<int> edges[222222];
int dfs(int par, int u) {
  vector<pair<int, int> > xv;
  unordered_map<int, int> v_to_x;
  for (int j = 0; j < edges[u].size(); j++) {
    int v = edges[u][j];
    if (par == v) continue;
    int x = dfs(u, v);
    if (x != -1) {
      xv.push_back(make_pair(x, v));
    }
    v_to_x[v] = x;
  }
  sort(xv.begin(), xv.end());
  unordered_set<int> discard;
  for (int j = 1; j < xv.size(); j++) {
    if (xv[j].first == xv[j - 1].first) discard.insert(xv[j].second);
  }
  vector<int> new_edges;
  int deg = 0;
  for (int j = 0; j < edges[u].size(); j++) {
    int v = edges[u][j];
    if (par == v) continue;
    if (discard.find(v) == discard.end()) {
      new_edges.push_back(v);
      deg++;
    }
  }
  if (par != -1) new_edges.push_back(par);
  edges[u] = new_edges;
  if (deg == 0) {
    return 1;
  } else if (deg == 1) {
    if (v_to_x[new_edges[0]] == -1)
      return -1;
    else
      return v_to_x[new_edges[0]] + 1;
  } else {
    return -1;
  }
}
void dfs2(int par, int u, vector<int>* verts) {
  verts->push_back(u);
  for (int j = 0; j < edges[u].size(); j++) {
    int v = edges[u][j];
    if (v == par) continue;
    dfs2(u, v, verts);
  }
}
int main() {
  int n;
  cin >> n;
  for (int i = 1; i <= n - 1; i++) {
    int u, v;
    cin >> u >> v;
    edges[u].push_back(v);
    edges[v].push_back(u);
  }
  vector<int> verts;
  for (int i = 1; i <= n; i++) verts.push_back(i);
  while (1) {
    int maxd = 0;
    int rt = -1;
    for (int id = 0; id < verts.size(); id++) {
      int i = verts[id];
      if (edges[i].size() > maxd) {
        rt = i;
        maxd = edges[i].size();
      }
    }
    if (maxd <= 2) break;
    dfs(-1, rt);
    int psize = verts.size();
    verts.clear();
    dfs2(-1, rt, &verts);
    if (verts.size() == psize) break;
  }
  int maxd = 0;
  for (int id = 0; id < verts.size(); id++)
    maxd = max(maxd, (int)edges[verts[id]].size());
  if (maxd > 2) {
    printf("-1\n");
    return 0;
  } else if (maxd == 1) {
    printf("%d\n", (int)verts.size() - 1);
  } else {
    int sz = verts.size();
    while (sz % 2 == 1) {
      sz = (sz + 1) / 2;
    }
    printf("%d\n", sz - 1);
  }
}
