#include <bits/stdc++.h>
using namespace std;
const long long mod = 1000000007;
template <typename T, typename U>
static void amin(T &x, U y) {
  if (y < x) x = y;
}
template <typename T, typename U>
static void amax(T &x, U y) {
  if (x < y) x = y;
}
int n, res;
vector<vector<int> > a;
vector<int> dp;
void dfs(int r, int p) {
  dp[r] = 1;
  for (int c : a[r]) {
    if (c != p) {
      dfs(c, r);
      if (dp[c] & 1) {
        dp[r] += dp[c];
      } else {
        ++res;
      }
    }
  }
}
int main() {
  scanf("%d", &n);
  a = vector<vector<int> >(n, vector<int>());
  dp = vector<int>(n);
  for (int i = 0; i < n - 1; i++) {
    int u, v;
    scanf("%d%d", &u, &v);
    u--;
    v--;
    a[u].push_back(v);
    a[v].push_back(u);
  }
  if (n & 1) {
    printf("%d", -1);
  } else {
    dfs(0, -1);
    printf("%d", res);
  }
}
