#include <bits/stdc++.h>
using namespace std;
using pii = pair<int, int>;
const int N = 2e5 + 10, inf = 3e5;
vector<int> adj[N];
pii mx[N][3];
int bad[N], p[N], up[N];
void add(int u, int d) {
  for (int i = 0; i < 3; i++)
    if (mx[u][i].first == d) {
      mx[u][i].second++;
      return;
    }
  if (mx[u][0].first < d) {
    mx[u][0] = {d, 1};
    sort(mx[u], mx[u] + 3);
  }
}
void dfs(int u, int fa = 0) {
  for (auto v : adj[u]) {
    if (v == fa) continue;
    p[v] = u;
    dfs(v, u);
    if (bad[v] || mx[v][1].first)
      bad[u]++;
    else
      add(u, mx[v][2].first + 1);
  }
}
bool update(int v, int u) {
  if (bad[u] > 1) return true;
  if (p[u] && !up[u]) return true;
  if (bad[u] == 1 && (!mx[v][1].first && !bad[v])) return true;
  pii a = mx[u][0], b = mx[u][1], c = mx[u][2];
  if (!bad[u]) {
    if (mx[v][2].first + 1 == a.first) a.second--;
    if (mx[v][2].first + 1 == b.first) b.second--;
    if (mx[v][2].first + 1 == c.first) c.second--;
  }
  if ((int)(a.second > 0) + (int)(b.second > 0) + (int)(c.second > 0) > 1)
    return true;
  if (p[u] && a.second && a.first != up[u]) return true;
  if (p[u] && b.second && b.first != up[u]) return true;
  if (p[u] && c.second && c.first != up[u]) return true;
  if (adj[u].size() == 1)
    up[v] = 1;
  else {
    if (p[u])
      up[v] = up[u] + 1;
    else if (a.second)
      up[v] = a.first + 1;
    else if (b.second)
      up[v] = b.first + 1;
    else if (c.second)
      up[v] = c.first + 1;
    else {
      cerr << "ERROR" << endl;
      exit(0);
    }
  }
  return false;
}
void redfs(int u, int fa = 0) {
  for (auto v : adj[u]) {
    if (v == fa) continue;
    if (update(v, u)) bad[v]++;
    redfs(v, u);
  }
}
int main() {
  int n;
  scanf("%d", &n);
  for (int i = 1; i < n; i++) {
    int u, v;
    scanf("%d %d", &u, &v);
    adj[u].push_back(v);
    adj[v].push_back(u);
  }
  dfs(1);
  redfs(1);
  int ans = inf;
  for (int i = 1; i <= n; i++) {
    if (bad[i]) continue;
    if (p[i] && !up[i]) continue;
    set<int> st;
    for (auto j : adj[i]) {
      if (j == p[i])
        st.insert(up[i]);
      else
        st.insert(mx[j][2].first + 1);
      if (st.size() > 2) break;
    }
    if (st.size() > 2) continue;
    int t = *st.begin() + *--st.end();
    while (t % 2 == 0) t /= 2;
    ans = min(ans, t);
  }
  if (ans == inf) ans = -1;
  cout << ans << endl;
  return 0;
}
