class Result {
  public static final int NUM_LETTERS = 26;
  /*
   * Complete the 'alternate' function below.
   *
   * The function is expected to return an INTEGER.
   * The function accepts STRING s as parameter.
   */

  public static int alternate(String s) {
    // Edge case: if length <= 1, no alternations are possible
    if (s.length() <= 1) {
      System.out.println(0);
      return 0;
    }
    // Flattened array to represent the upper triangular portion of the matrix
    int[] count = new int[(NUM_LETTERS * (NUM_LETTERS - 1)) / 2];
    char[] lastSeen = new char[(NUM_LETTERS * (NUM_LETTERS - 1)) / 2];
    // Helper function to calculate the index in the flattened array

    // Process the string
    for (char c : s.toCharArray()) {
      int charIndex = c - 'a';

      // Update all pairs involving this character
      for (int i = 0; i < NUM_LETTERS; i++) {
        if (i == charIndex)
          continue;

        int index =
            charIndex < i ? getIndex(charIndex, i) : getIndex(i, charIndex);

        if (count[index] != -1) { // Only process if valid
          if (lastSeen[index] == c) {
            count[index] = -1; // Invalidate if repeating
          } else {
            lastSeen[index] = c; // Update last seen character
            count[index]++;
          }
        }
      }
    }

    // Find the maximum valid count
    int max = 0;
    for (int c : count) {
      max = Math.max(max, c);
    }
    return max;
  }
  private static int getIndex(int i, int j) {
    return i * NUM_LETTERS + j - ((i + 1) * (i + 2)) / 2;
  }
}