Merkkijono

def s(n, middle_index):
    if n == 1:
        return str(middle_index)
    return s(n-1, middle_index+1)+str(middle_index)+s(n-1, middle_index+1)

def convert(s):
    letters = "abcdefghijklmnopqrstuvwxyz"
    return "".join([letters[int(i)] for i in s])

print(convert((s(int(input()), 0))))

if __name__ == "__main__" and False:
    for i in range(1, 5):
        print(convert((s(i, 0))))

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: WRONG ANSWER

Test 12

Verdict: WRONG ANSWER

Test 13

Verdict: WRONG ANSWER

Test 14

Verdict: WRONG ANSWER

Test 15

Verdict: WRONG ANSWER

Test 16

Verdict: WRONG ANSWER