#include <bits/stdc++.h>
using namespace std;
const int N = 200005;
struct node {
  int to, next;
} p[N << 2];
int head[N], tot, n, now[N], du[N];
bool vis[N], isok;
vector<pair<int, int> > a;
void add(int x, int y) {
  p[++tot] = (node){y, head[x]};
  head[x] = tot;
  p[++tot] = (node){x, head[y]};
  head[y] = tot;
}
inline void del(int x, int fa) {
  du[fa]--;
  vis[x] = 1;
  for (int i = head[x]; i; i = p[i].next) {
    int y = p[i].to;
    if (vis[y] || y == fa) continue;
    del(y, x);
  }
}
inline void dfs(int x, int fa) {
  int son = 0, id = 0;
  for (int i = head[x]; i; i = p[i].next) {
    int y = p[i].to;
    if (vis[y] || y == fa) continue;
    dfs(y, x);
    if (~now[y])
      son++, id = y;
    else
      son += 2;
  }
  if (!son) {
    now[x] = 1;
    return;
  }
  if (son == 1) {
    now[x] = (~now[id] ? now[id] : -2) + 1;
    return;
  }
  a.clear();
  for (int i = head[x]; i; i = p[i].next) {
    int y = p[i].to;
    if (vis[y] || y == fa || now[y] == -1) continue;
    a.push_back(make_pair(now[y], y));
  }
  sort(a.begin(), a.end());
  int m = a.size();
  for (int i = 0; i < m; i++) {
    int r = i;
    while (r < m && a[r].first == a[i].first) r++;
    for (int j = i + 1; j < r; j++) del(a[j].second, x), isok = 1;
    i = r - 1;
  }
  now[x] = -1;
}
int check() {
  for (int i = 1; i <= n; i++)
    if (du[i] > 2) return i;
  return -1;
}
int main() {
  scanf("%d", &n);
  for (int i = 1; i < n; i++) {
    int x, y;
    scanf("%d%d", &x, &y);
    add(x, y);
    du[x]++;
    du[y]++;
  }
  while (1) {
    int root = check();
    isok = 0;
    if (root == -1) break;
    dfs(root, -1);
    if (!isok) break;
  }
  if (check() == -1) {
    int ans = n - 1;
    for (int i = 1; i <= n; i++) ans -= vis[i];
    while (ans % 2 == 0) ans /= 2;
    printf("%d\n", ans);
  } else
    puts("-1");
  return 0;
}
