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 long maxn = 2e5 + 55;
long long sub[maxn], cnt = -1;
vector<long long> graph[maxn];
long long dfs(long long curr, long long pre) {
  map<long long, long long> memo;
  long long ans = -1, num = 0;
  for (long long i = 0; i < graph[curr].size(); i++) {
    if (graph[curr][i] == pre) continue;
    long long p = dfs(graph[curr][i], curr);
    num = p;
    memo[p]++;
    if (memo[p] > 1) {
      if (p > ans) ans = p;
    }
  }
  if (ans != -1) {
    if (cnt < ans + 1) cnt = ans + 1;
    return -1;
  }
  if (graph[curr].size() > 2 || num == -1) return -1;
  return num + 1;
}
long long main() {
  long long n;
  cin >> n;
  for (long long i = 1; i < n; i++) {
    long long u, v;
    cin >> u >> v;
    graph[u].push_back(v);
    graph[v].push_back(u);
  }
  for (long long i = 1; i <= n; i++) {
    dfs(i, -1);
  }
  cout << cnt << endl;
}
