seti_2

#include<bits/stdc++.h>

#define endl "\n"
using namespace std;
using ll = long long;
using ld = long double;
using pii = pair<int, int>;

constexpr int N = 1e2 + 5;

vector<int> gr[N];
vector<bool> used;
int dist[N][N];
string s;

int find_diam() {
  for (int k = 0; k < N; k++)
    for (int i = 0; i < N; i++)
      for (int j = 0; j < N; j++)
        if (i != j && j != k && i != k)
          dist[i][j] = min(dist[i][j], dist[i][k] + dist[k][j]);
  int ans = 0;
  for (int i = 0; i < N; i++)
    for (int j = 0; j < N; j++)
      ans = max(dist[i][j] == N ? 0: dist[i][j], ans);
  return ans;
}

void add_edge(int a, int b) {
  dist[a][b] = 1;
  dist[b][a] = 1;
}

void Solve() {
  fill(&dist[0][0], &dist[N - 1][N], N);
  getline(cin, s);
  for (int i = 0; i < s.size();) {
    while(i < s.size() && !isdigit(s[i]))
      i++;
    string n1, n2;
    while(i < s.size() && isdigit(s[i]))
      n1.push_back(s[i]), i++;
    while(i < s.size() && !isdigit(s[i]))
      i++;
    while(i < s.size() && isdigit(s[i]))
      n2.push_back(s[i]), i++;
    if (n1.size() && n2.size())
      add_edge(stoi(n1), stoi(n2));
  }
  cout << find_diam();
}

int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  cout.tie(nullptr);
  //auto start = chrono::high_resolution_clock::now();
  Solve();
  //auto end = chrono::high_resolution_clock::now();
  //cout << endl << (chrono::duration_cast<chrono::duration<double>>(end - start)).count();
  return 0;
}