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 = 2e5 + 5, M = 1e7 + 5, K = 25;
vector<int> g[N];
int root, mx, center;
vector<int> tmp;
set<int> depths;
void dfs(int node, int parent, int depth) {
  if (g[node].size() == 1 && parent != node) depths.insert(depth);
  tmp.push_back(node);
  if (depth > mx) {
    mx = depth;
    root = node;
    center = tmp[tmp.size() / 2];
  }
  for (auto child : g[node]) {
    if (child == parent) continue;
    dfs(child, node, depth + 1);
  }
  tmp.pop_back();
}
int main() {
  ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0);
  int n;
  cin >> n;
  for (int i = 1; i < n; i++) {
    int x, y;
    cin >> x >> y;
    g[x].push_back(y);
    g[y].push_back(x);
  }
  mx = 0;
  dfs(1, 1, 0);
  mx = 0;
  dfs(root, root, 0);
  depths.clear();
  dfs(center, center, 0);
  if (depths.size() > 2) return cout << -1, 0;
  int ans = *depths.begin();
  if (depths.size() == 2) ans += *depths.rbegin();
  if (ans % 2 == 0) ans = 1;
  cout << ans;
  return 0;
}
