10
4 2
7 4
2 6
2 5
4 8
10 3
2 9
9 1
5 10
 10
5 10
7 8
8 3
2 6
3 2
9 7
4 5
10 1
6 4
 4
4 1
4 3
4 2
 3
3 1
1 2
 9
1 2
1 3
1 4
1 5
1 6
6 7
6 8
8 9
 5
1 5
2 3
2 4
1 2
 8
6 1
4 7
4 8
8 5
7 6
4 3
4 2
 7
5 6
5 7
5 1
7 4
6 3
3 2
 3
1 3
3 2
 2
1 2
 5
5 4
4 3
3 1
5 2
 6
1 6
3 1
6 4
5 3
2 5
 11
8 9
2 7
1 11
3 2
9 1
8 5
8 6
5 4
4 10
8 3
 11
11 9
6 7
7 1
8 11
5 6
3 5
9 3
10 8
2 4
4 10
 12
12 6
6 7
8 11
4 8
10 4
12 3
2 10
6 2
12 9
4 1
9 5

-1
 9
 1
 1
 3
 3
 -1
 -1
 1
 1
 1
 5
 1
 5
 -1

#include <bits/stdc++.h>
using namespace std;
int to[200100], nex[200100], beg[100100], rd[200100], dis[100100] = {-1};
bool done[200100];
set<int> bian[100100];
int n, ans, len;
int maxx, place;
inline void Add_edge(int a, int b) {
  nex[++len] = beg[a], beg[a] = len, to[len] = b;
  nex[++len] = beg[b], beg[b] = len, to[len] = a;
}
void get_gen1(int p, int fa) {
  dis[p] = dis[fa] + 1;
  for (int i = beg[p]; i; i = nex[i]) {
    if (to[i] != fa) get_gen1(to[i], p);
  }
  if (dis[p] > maxx) maxx = dis[p], place = p;
}
int dfs(int p, int fa, int dis) {
  int last = 0, f = 0;
  for (int i = beg[p]; i; i = nex[i]) {
    if (to[i] != fa) {
      int tmp = dfs(to[i], p, dis + 1);
      if (bian[p].count(tmp)) last = 0, ans += tmp;
      last = tmp;
      if (tmp != -1 && (!bian[p].count(tmp))) bian[p].insert(tmp);
      if (tmp == -1) f = 1;
    }
  }
  if (bian[p].size() > 1 || f) return -1;
  return last + 1;
}
int main() {
  scanf("%d", &n);
  for (int i = 1, a, b; i < n; i++) {
    scanf("%d%d", &a, &b);
    rd[a]++, rd[b]++;
    Add_edge(a, b);
  }
  for (int i = 1; i <= n; i++) {
    if (rd[i] == 1) {
      get_gen1(i, 0);
      break;
    }
  }
  memset(dis, -1, sizeof(dis));
  maxx = 0;
  get_gen1(place, 0);
  int tmp = (dis[place] + 1) / 2;
  while (tmp--) {
    for (int i = beg[place]; i; i = nex[i])
      if (dis[place] == dis[to[i]] + 1) place = to[i];
  }
  dfs(place, 0, 0);
  if (!ans)
    printf("-1\n");
  else
    printf("%d\n", n - ans - 1);
  return 0;
}
