#include <bits/stdc++.h>
using namespace std;
const int maxn = 1e5 + 5;
struct Edge {
  int to;
  Edge *nxt;
} * arc[maxn], pool[maxn << 1];
int n, ecnt, ans;
bool vis[maxn];
int getint() {
  char ch;
  int ret = 0, p;
  while (!isdigit(ch = getchar()) && (ch ^ '-'))
    ;
  p = ch == '-' ? ch = getchar(), -1 : 1;
  while (isdigit(ch)) ret = (ret << 3) + (ret << 1) + (ch ^ 48), ch = getchar();
  return ret * p;
}
Edge *newedge() { return &pool[ecnt++]; }
void AddEdge(int u, int v) {
  Edge *pedge = newedge();
  pedge->to = v;
  pedge->nxt = arc[u];
  arc[u] = pedge;
}
int dfs(int x) {
  vis[x] = true;
  int cnt = 1;
  for (Edge *e = arc[x]; e != NULL; e = e->nxt) {
    int v = e->to;
    if (!vis[v]) {
      int tmp = dfs(v);
      if (!(tmp & 1)) ans++;
      cnt += tmp;
    }
  }
  return cnt;
}
int main() {
  n = getint();
  for (int i = 1; i < n; i++) {
    int u = getint(), v = getint();
    AddEdge(u, v);
    AddEdge(v, u);
  }
  if (n & 1) {
    printf("-1");
    return 0;
  }
  dfs(1);
  printf("%d\n", ans);
  return 0;
}
