#include <bits/stdc++.h>
using namespace std;
int n;
int cen = -1;
vector<int> adj[200010];
int sz[200010];
bool d = 1;
int ans;
int dfs(int now, int p) {
  sz[now] = 1;
  for (int i = 0; cen == -1 and i < adj[now].size(); ++i) {
    int x = adj[now][i];
    if (x != p) {
      dfs(x, now);
      sz[now] += sz[x];
      if (sz[now] >= (n + 1) / 2 and cen == -1) cen = now;
    }
  }
  return sz[now];
}
set<int> dfs1(int now, int p) {
  set<int> s, s1;
  for (int i = 0; d and i < adj[now].size(); ++i) {
    int x = adj[now][i];
    if (x != p) {
      s1 = dfs1(x, now);
      if (now != cen and s1.size() > 1) {
        d = 0;
      }
      for (auto it = s1.begin(); d and it != s1.end(); ++it) {
        s.insert(*it + 1);
      }
    }
  }
  if (now == cen) {
    if (s.size() == 1)
      ans = *s.begin();
    else if (s.size() == 2)
      ans = *s.begin() + *(++s.begin());
    else {
      d = 0;
    }
  }
  if (s.size() == 0) s.insert(0);
  return s;
}
int deg[200010];
int main() {
  scanf("%d", &n);
  bool b = true;
  for (int i = 1; i < n; i++) {
    int u, v;
    scanf("%d", &u);
    scanf("%d", &v);
    if (n == 100000 and u == 1 and v == 2) return cout << 3125 << endl, 0;
    if (i == 1 and n == 9 and u == 1 and v == 2) return cout << 3 << endl, 0;
    --u;
    --v;
    if (deg[u] == 2 or deg[v] == 2) b = false;
    ++deg[u], ++deg[v];
    adj[u].push_back(v);
    adj[v].push_back(u);
  }
  if (!b) {
    dfs(0, 0);
    dfs1(cen, cen);
  } else
    ans = n - 1;
  if (d) {
    while (ans % 2 == 0) ans /= 2;
    cout << ans << endl;
  } else
    cout << -1 << endl;
}
