#include <bits/stdc++.h>
using namespace std;
using ll = long long;
template <typename Arg1>
void __f(const char* name, Arg1&& arg1) {
  cout << name << " : " << arg1 << endl;
}
template <typename Arg1, typename... Args>
void __f(const char* names, Arg1&& arg1, Args&&... args) {
  const char* comma = strchr(names + 1, ',');
  cout.write(names, comma - names) << " : " << arg1 << " | ";
  __f(comma + 1, args...);
}
const ll mod = 1e9 + 7;
const ll N = 1e5 + 5;
ll cnt = 0;
vector<ll> adj[N];
ll ans[N];
void dfs(ll node, ll parent) {
  ans[node] = 1;
  for (ll child : adj[node]) {
    if (child == parent) continue;
    dfs(child, node);
    if (ans[child] % 2 == 0) cnt++;
    ans[node] += ans[child];
  }
}
void run_case() {
  ll n, u, v;
  cin >> n;
  for (ll i = 0; i < n - 1; i++) {
    cin >> u >> v;
    adj[u].push_back(v);
    adj[v].push_back(u);
  }
  if (n & 1) {
    cout << -1 << endl;
    return;
  }
  dfs(1, 0);
  cout << cnt << endl;
}
int32_t main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  ll tc = 1;
  for (ll t = 1; t <= tc; t++) {
    run_case();
  }
}
