#include <bits/stdc++.h>
using namespace std;
long long pre[26][100005], suff[26][100005];
int main() {
  string s;
  cin >> s;
  int n = s.length();
  if (n == 1) {
    cout << 1 << endl;
    return 0;
  }
  if (n == 2) {
    if (s[0] == s[1]) {
      cout << 2 << endl;
      return 0;
    }
    cout << 1 << endl;
    return 0;
  }
  for (int i = 0; i < n; i++) {
    if (i != 0) {
      for (int j = 0; j < 26; j++) {
        pre[j][i] = pre[j][i - 1];
      }
    }
    int ind = s[i] - 'a';
    pre[ind][i]++;
  }
  long long ans = 0;
  map<string, long long> m;
  for (int i = 1; i < n; i++) {
    string temp = "";
    for (int j = 0; j < 26; j++) {
      temp.push_back('a' + j);
      temp.push_back(s[i]);
      m[temp] += pre[j][i - 1];
    }
  }
  for (auto it = m.begin(); it != m.end(); it++) {
    ans = max(ans, it->second);
  }
  for (int i = 0; i < 26; i++) {
    ans = max(ans, pre[i][n - 1]);
  }
  cout << ans << endl;
}
