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 INF = 0x3f3f3f3f;
const double PI = acos(-1.0);
void no() {
  cout << -1 << endl;
  exit(0);
}
const int N = 2e5 + 5;
int n;
vector<int> g[N];
bool f = 1;
int res = INF;
map<pair<int, int>, int> ans;
void go(int pai, int at, int sz) {
  if (g[at].size() > 2) {
    f = 0;
    ans[pair<int, int>(at, sz)]++;
    if (ans[pair<int, int>(at, sz)] >= 2) res = min(res, sz);
    return;
  }
  for (int i = 0; i < (int)g[at].size(); i++) {
    int next = g[at][i];
    if (next == pai) continue;
    go(at, next, sz + 1);
  }
}
int main(void) {
  ios_base::sync_with_stdio(false);
  cin >> n;
  for (int i = 1; i < n; i++) {
    int a, b;
    cin >> a >> b;
    g[a].push_back(b);
    g[b].push_back(a);
  }
  for (int i = 1; i <= n; i++)
    if (g[i].size() == 1) go(-1, i, 1);
  if (f) {
    if (n % 2) {
      cout << (n / 2) + 1 << endl;
      return 0;
    } else
      no();
  }
  if (res == INF) no();
  cout << res << endl;
  return 0;
}
