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 N = 200005;
int maxlevel = 0;
int level[N];
int degree[N];
vector<int> vx[N];
set<int> c;
queue<int> q;
int n, center;
int f(int v, int p) {
  if (vx[v].size() == 1 && v != center) return 0;
  set<int> S;
  for (auto x : vx[v])
    if (x != p) {
      int q = f(x, v);
      if (q == -1) return -1;
      S.insert(q);
    }
  if (v != center && S.size() != 1) return -1;
  if (v != center) return 1 + *(S.begin());
  if (S.size() == 1) return 1 + *(S.begin());
  if (S.size() == 2) {
    int sum = 0;
    for (auto x : S) sum += x;
    return 2 + sum;
  }
  return -1;
}
int main() {
  cin >> n;
  int a, b;
  for (int i = 0; i < n - 1; ++i) {
    cin >> a >> b;
    vx[a].push_back(b);
    vx[b].push_back(a);
    degree[a]++;
    degree[b]++;
  }
  if (n == 2) {
    cout << 1;
    return 0;
  }
  for (int i = 0; i < N; i++) {
    if (degree[i] == 1) {
      q.push(i);
    }
  }
  while (!q.empty()) {
    int v = q.front();
    q.pop();
    for (auto x : vx[v]) {
      degree[x]--;
      if (degree[x] == 1) {
        q.push(x);
        level[x] = level[v] + 1;
        maxlevel = max(maxlevel, level[x]);
      }
    }
  }
  for (int i = 0; i < N; i++) {
    if (level[i] == maxlevel) {
      c.insert(i);
    }
  }
  center = *(c.begin());
  cout << f(center, 0);
  return 0;
}
