Merkkijono

import java.util.Scanner;

public class Toka {
    public static Scanner sc = new Scanner(System.in);
    public static void main(String[] args) {
        int n = Integer.parseInt(sc.nextLine())-1;
        String[] alphabet = "abcdefghijklmnop".split("");

        int size = 0;
        for (int i = 0; i <= n; i++) {
            size+=Math.pow(2,i);
        }

        String p = "";
        for (int i = 1; i < size+1; i++) {
            for (int k = n; k >= 0; k--) {
                if (i%Math.pow(2,k)==0) {
                    p+=alphabet[n-k];
                    break;
                }
            }
        }
        System.out.println(p);
    }
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: ACCEPTED

Test 7

Verdict: ACCEPTED

Test 8

Verdict: ACCEPTED

Test 9

Verdict: ACCEPTED

Test 10

Verdict: ACCEPTED

Test 11

Verdict: ACCEPTED

Test 12

Verdict: ACCEPTED

Test 13

Verdict: ACCEPTED

Test 14

Verdict: ACCEPTED

Test 15

Verdict: ACCEPTED

Test 16

Verdict: ACCEPTED