public class SolutionA {


    public static void main(String[] args) {

        char[] letters = {'A','B','C','D','E','F','G','H','I'};
        char[] password = new char[4];
        int[] pos = new int[4];

        for(int i = 0; i<4;i++){
            pos[i] = 0;
        }

        boolean running = true;

        while(running){
            //i < n
            for(int i= 0; i < 4; i++){

                //i == n-1
                if(i == 3) {
                    password[i] = letters[pos[i]++];

                    if(pos[i] == letters.length) {
                        for(int j = 3; j>=0; j--) {

                            if((j !=3 &&  pos[j] != letters.length-1) || (j == 3 && pos[j] != letters.length)) {
                                pos[j]++;
                                break;
                            }
                            else if(j == 0 && pos[j] == letters.length-1) {
                                running = false;
                            }
                            else {
                                pos[j] = 0;
                            }
                        }
                    }
                }

                else {
                    password[i] = letters[pos[i]];
                }
            }
            boolean correct = true;
            if(password[0] != 'D' && password[0] != 'H' ) {
                correct = false;
            }
            for(int i = 0; i<4;i++){
                if(i <3){
                    if(password[i] == 'G' && password[i+1] == 'A'){
                        correct =false;
                    }
                    else if(password[i] == 'A' && password[i+1] == 'G'){
                        correct = false;
                    }
                }
            }

            for(int i = 0; i<4;i++){
                if(i <3){
                    if(password[i] == 'B' && (password[i+1] != 'B' && password[i+1] != 'C')){
                        correct =false;
                    }
                }
            }

            if(correct) {
                System.out.println(password);
            }
        }
    }
}