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 long double EPS = 1e-9, PI = acos(-1.);
const int INF = 0x3f3f3f3f, MOD = 1e9 + 7;
const int N = 2e5 + 5;
int n, a, b, inc[N], np[N], vis[N], h[N];
vector<int> adj[N];
map<int, int> mp[N];
int main() {
  scanf("%d", &n);
  for (int i = 0; i < n - 1; ++i) {
    scanf("%d%d", &a, &b);
    adj[a].push_back(b);
    adj[b].push_back(a);
    inc[a]++, inc[b]++;
  }
  int ok = 1;
  for (int i = 1; i <= n and ok; ++i)
    if (inc[i] > 2) ok = 0;
  if (ok) return 0 * printf("%d\n", n - 1);
  queue<int> q;
  for (int i = 1; i <= n; ++i)
    if (inc[i] < 2) q.push(i), mp[i][0] = 1;
  while (q.size()) {
    int u = q.front();
    q.pop();
    vis[u] = 1;
    if (!inc[u]) {
      if (np[u]) break;
      if (mp[u].size() > 2) break;
      if (mp[u].size() == 2) {
        int ans = 0;
        for (auto x : mp[u]) ans += x.first;
        return 0 * printf("%d\n", ans);
      }
      return 0 * printf("%d\n", 2 * (mp[u].begin())->first);
    }
    if (!np[u]) {
      if (mp[u].size() > 1)
        np[u] = 1;
      else
        h[u] = (mp[u].begin())->first;
    }
    for (int v : adj[u])
      if (!vis[v]) {
        np[v] |= np[u];
        mp[v][h[u] + 1]++;
        inc[v]--;
        if (inc[v] == 1) q.push(v);
      }
  }
  printf("-1\n");
  return 0;
}
