#include <bits/stdc++.h>
using namespace std;
int n;
vector<int> g[100500];
pair<bool, int> dp[100500];
void dfs(int v, int p = -1) {
  int res = 0;
  bool even = false;
  for (int u : g[v])
    if (u != p) {
      dfs(u, v);
      res += dp[u].second;
      if (!dp[u].first)
        even = !even;
      else
        res++;
    }
  dp[v] = {even, res};
}
int main() {
  ios::sync_with_stdio(0);
  cin.tie();
  cout.tie();
  cin >> n;
  for (int i = 0; i < n; i++) dp[i] = {-1, -1};
  for (int i = 0; i < n - 1; i++) {
    int x, y;
    cin >> x >> y;
    g[x - 1].push_back(y - 1);
    g[y - 1].push_back(x - 1);
  }
  dfs(0);
  if (dp[0].first)
    cout << dp[0].second;
  else
    cout << -1;
  return 0;
}
