public static int gemstones(List<String> arr) {
    // Write your code here
    String alphabetsStr = "abcdefghijklmnopqrstuvwxyz";
    int count = alphabetsStr.length();
    
    for(Character c: alphabetsStr.toCharArray()){
        int flag=0;
        for(String s : arr){
            if(!s.contains(String.valueOf(c))){
                flag=1;
                break;
            }
        }
        if(flag==1)
            count--;
    }
    return count;

    }