Merkkijono

import string

def muodosta_jono(n):
    jono = ["a"]
    for i in range(n-1):
        uusi_jono = ["0"]*(len(jono)*2+1)
        for j in range(len(uusi_jono)):
            if j%2 == 1:
                uusi_jono[j] = jono[(j-1)//2]
            else:
                uusi_jono[j] = string.ascii_lowercase[i+1]
        #print("jono", "".join(uusi_jono))
        jono = uusi_jono
    
    return "".join(jono)

n = int(input())
print(muodosta_jono(n))

if __name__ == "__main__" and False:
    for i in range(1, 6):
        print(muodosta_jono(i))

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