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 int maxn = 2e5 + 10;
vector<int> seq;
bool tk[maxn];
int n;
set<int> G[maxn], Set[maxn];
int main() {
  scanf("%d", &n);
  for (int i = 0; i < n - 1; i++) {
    int u, v;
    scanf("%d%d", &u, &v);
    G[u].insert(v);
    G[v].insert(u);
  }
  for (int i = 1; i <= n; i++)
    if (G[i].size() == 1) tk[i] = true, seq.push_back(i);
  for (int i = 0; i < seq.size(); i++) {
    int u = seq[i];
    if (i == n - 1) {
      if (Set[u].size() > 2) break;
      int sum = 0;
      for (auto it = Set[u].begin(); it != Set[u].end(); it++) sum += *it;
      return !printf("%d\n", sum & 1 ? sum : sum / 2);
    }
    if (Set[u].size() > 1) continue;
    int cur = Set[u].empty() ? 0 : *Set[u].begin();
    for (auto it = G[u].begin(); it != G[u].end(); it++) {
      int v = *it;
      G[v].erase(u);
      Set[v].insert(cur + 1);
      if (!tk[v] && G[v].size() <= 1 &&
          (Set[v].size() <= 1 || seq.size() == n - 1))
        tk[v] = true, seq.push_back(v);
    }
  }
  printf("-1");
  return 0;
}
