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 PI = acos(-1);
const double EPS = 1e-9;
const int inf = 1e8;
int dx[4] = {0, 1, 0, -1};
int dy[4] = {1, 0, -1, 0};
int main() {
  int n;
  cin >> n;
  vector<vector<long long> > G(n);
  for (int i = 0; i < n - 1; i++) {
    int a, b;
    cin >> a >> b;
    a--;
    b--;
    G[a].push_back(b);
    G[b].push_back(a);
  }
  vector<long long> dame(n);
  while (1) {
    vector<long long> ha;
    for (int i = 0; i < n; i++)
      if (G[i].size() == 1 && dame[i] == 0) {
        ha.push_back(-1);
        ha.push_back(i);
      }
    bool h = true;
    while (ha.size()) {
      vector<long long> nha;
      vector<long long> ok(n);
      for (int i = 0; i < ha.size(); i++) {
        int TO = -1, co = 0, pre = ha[i];
        i++;
        for (int j = 0; j < G[ha[i]].size(); j++) {
          int to = G[ha[i]][j];
          if (pre == to || dame[to]) continue;
          co++;
          TO = to;
        }
        if (co == 1) {
          if (ok[TO] == 0) {
            ok[TO] = true;
            nha.push_back(ha[i]);
            nha.push_back(TO);
          } else {
            h = false;
            int now = ha[i];
            dame[now] = true;
            while (1) {
              for (int q = 0; q < G[now].size(); q++)
                if (TO != G[now][q] && dame[G[now][q]] == 0) {
                  now = G[now][q];
                  dame[now] = true;
                  goto end;
                }
              break;
            end:;
            }
          }
        }
      }
      ha = nha;
    }
    break;
    if (!h) break;
  }
  int out = 0;
  for (int i = 0; i < n; i++)
    if (dame[i] == 0) out++;
  if (out == n)
    cout << -1 << endl;
  else
    cout << out - 1 << endl;
}
