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;
const double eps = 1e-8;
const double pi = acos(-1.0);
const int K = 2e5 + 7;
const int mod = 1e9 + 7;
int n, d[K], mx, sum[2 * K], m;
vector<int> mp[K];
int dfs(int x, int f) {
  int a[3], num = 0;
  for (int i = 0; i < mp[x].size(); i++)
    if (mp[x][i] != f) {
      int v = mp[x][i];
      a[2] = dfs(v, x);
      if (a[2] == -1) return -1;
      if (num == 0)
        a[0] = a[2], num++;
      else if (num == 1) {
        if (a[0] != a[2]) num++, a[1] = a[2];
      } else {
        if (a[0] != a[2] && a[1] != a[2]) return -1;
      }
    }
  if (x != mx) {
    if (num == 2)
      return -1;
    else if (num == 1)
      return a[0] + 1;
    return 1;
  }
  if (num == 2)
    return a[0] + a[1];
  else
    return a[0];
}
int main(void) {
  cin >> n;
  for (int i = 1, u, v; i < n; i++) {
    scanf("%d%d", &u, &v);
    mp[u].push_back(v), mp[v].push_back(u);
    d[u]++, d[v]++;
    if (d[u] > d[mx]) mx = u;
    if (d[v] > d[mx]) mx = v;
  }
  for (int i = 1; i <= n && n % 2 == 1; i++) sum[d[i]]++;
  for (int i = 1; i <= n && n % 2 == 1; i++)
    if (sum[i]) m++;
  if (n % 2 == 1 && m == 2 && sum[1] == 2 && sum[2] == n - 2)
    printf("%d\n", n / 2);
  else
    printf("%d\n", dfs(mx, 0));
  return 0;
}
