#include <bits/stdc++.h>
using namespace std;
vector<int> e[(int)1e5 + 1];
bool v[(int)1e5 + 1];
int p[(int)1e5 + 1];
int sz[(int)1e5 + 1];
int ans = 0;
int ufind(int now) {
  if (now == p[now]) return now;
  return p[now] = ufind(p[now]);
}
int go(int now) {
  sz[now] = 1;
  for (int i = 0; i < e[now].size(); i++) {
    int next = e[now][i];
    if (v[next]) continue;
    v[next] = true;
    p[next] = now;
    sz[now] += go(next);
  }
  return sz[now];
}
int go2(int now) {
  for (int i = 0; i < e[now].size(); i++) {
    int next = e[now][i];
    if (v[next]) continue;
    v[next] = true;
    if (sz[p[now]] % 2 == 0 && sz[next] % 2 == 0) {
      sz[p[now]] -= sz[next];
      p[next] = next;
      ans++;
    } else
      p[next] = ufind(now);
    go2(next);
  }
}
int main() {
  int n;
  cin >> n;
  if (n % 2 == 1) {
    cout << "-1\n";
    return 0;
  }
  for (int i = 0; i < n - 1; i++) {
    int u, v;
    cin >> u >> v;
    e[u].push_back(v);
    e[v].push_back(u);
  }
  v[1] = true;
  p[1] = 1;
  go(1);
  memset(v, 0, sizeof(v));
  v[1] = true;
  go2(1);
  cout << ans << "\n";
}
