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-6;
const double pi = acos(-1.0);
const long long mod = 1e18 + 7;
const int INF = 0x3f3f3f3f;
string s;
vector<int> v[200010], ans[200010];
int vis[200010], cnt[200010];
void dfs(int x, int m) {
  ans[x].push_back(m);
  if (((int)(v[x]).size()) >= 3) {
    return;
  }
  for (auto i : v[x]) {
    if (!vis[i]) {
      vis[i] = 1;
      dfs(i, m + 1);
      vis[i] = 0;
    }
  }
}
int main() {
  int n, a, b;
  cin >> n;
  for (int i = 1; i < n; i++) {
    scanf("%d%d", &a, &b);
    v[a].push_back(b);
    v[b].push_back(a);
    cnt[a]++;
    cnt[b]++;
  }
  for (int i = 1; i <= n; i++) {
    if (cnt[i] == 1) {
      vis[i] = 1;
      dfs(i, 1);
      vis[i] = 0;
    }
  }
  int res = n;
  for (int i = 1; i <= n; i++) {
    sort((ans[i]).begin(), (ans[i]).end());
    int l = ((int)(ans[i]).size());
    if (l)
      for (int j = 1; j < l; j++) {
        if (ans[i][j] == n) {
          cout << (n + 1) / 2 << endl;
          return 0;
        }
        if (ans[i][j] == ans[i][j - 1]) res -= ans[i][j];
      }
  }
  if (res == n)
    puts("-1");
  else
    cout << res << endl;
  return 0;
}
