import java.util.ArrayList;
import java.util.List;

class Solution {

    // ArrayList to store the masks of valid strings
    static ArrayList<Integer> masks;

    public int maxLength(List<String> arr) {
        masks = new ArrayList<>();

        // Iterating through the input strings and get their masks, add valid masks to the ArrayList
        for (String s : arr) {
            int mask = getMask(s);
            if (mask != -1) {
                masks.add(mask);
            }
        }

        // Calling the DFS function starting from index 0 with an initially empty set
        return dfs(0, 0);
    }

    // DFS function to explore all possible combinations of masks
    static int dfs(int s, int used) {
        // Initialize the result with the count of set bits in the 'used' mask
        int res = Integer.bitCount(used);

        // Iterating through the masks and explore valid combinations
        for (int i = s; i < masks.size(); i++) {
            // Checking if the current mask can be added to the combination
            if ((used & masks.get(i)) == 0) {
                // Updating the result with the maximum length obtained by adding the current mask
                res = Math.max(res, dfs(i + 1, used | masks.get(i)));
            }
        }
        return res;
    }

    // Helper function to get the mask of a string, returns -1 if the string has duplicate characters
    static int getMask(String s) {
        int mask = 0;
        for (char c : s.toCharArray()) {
            int i = c - 'a';
            // Checking for duplicate characters in the string
            if ((mask & (1 << i)) != 0) {
                return -1;
            }
            // Set the corresponding bit for the character in the mask
            mask |= 1 << i;
        }
        return mask;
    }
}