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 dy[] = {1, -1, 0, 0, -1, 1, 1, -1};
int dx[] = {0, 0, 1, -1, 1, -1, 1, -1};
void file() {}
void fast() {
  std::ios_base::sync_with_stdio(0);
  cin.tie(NULL);
}
const int N = 2e5 + 9;
int n;
bool no;
vector<int> adjL[N];
int solve(int u, int par) {
  set<int> st;
  int hold = par;
  for (auto v : adjL[u]) {
    if (v == par) continue;
    hold = v;
    st.insert(solve(v, u));
  }
  if ((int)(st.size()) == 1) {
    adjL[u] = vector<int>(1, hold);
    return *st.begin() + 1;
  } else if (st.empty())
    return 1;
  if (par != -1)
    no = 1;
  else if ((int)(st.size()) > 2)
    no = 1;
  if (par == -1) {
    int ans = 1;
    for (auto it : st) ans += it;
    return ans;
  }
  return 5;
}
int main() {
  file();
  fast();
  cin >> n;
  for (int i = 0; i < n - 1; i++) {
    int u, v;
    cin >> u >> v;
    adjL[u].push_back(v);
    adjL[v].push_back(u);
  }
  int root = 0;
  for (int i = 1; i <= n; i++)
    if ((int)(adjL[i].size()) > (int)(adjL[root].size())) root = i;
  int ans = solve(root, -1);
  if (no) return cout << -1 << "\n", 0;
  cout << ans - 1 << "\n";
  return 0;
}
