Merkkijono

x = int(input())
aakkoset = ["a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n", "o",
            "p", "q", "r", "s", "t", "u", "v", "w", "x", "y", "z"]


parilliset = list(range(0,100,2))
merkkijono = []
if x == 0:
    print("a")
else:
    for a in range(x):
        if a == 0:
            merkkijono.append("a")
        else:
            for b in range(len(merkkijono)):
                merkkijono.insert(parilliset[b], aakkoset[a])
    merkkijono_loppu = merkkijono
    merkkijono_loppu.reverse()
    merkkijono = merkkijono + merkkijono_loppu
    merkkijono.remove("a")
    print("".join(merkkijono))

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: RUNTIME ERROR

Traceback (most recent call last):
  File "input/code.py", line 16, in <module>
    merkki...

Test 9

Verdict: RUNTIME ERROR

Traceback (most recent call last):
  File "input/code.py", line 16, in <module>
    merkki...

Test 10

Verdict: RUNTIME ERROR

Traceback (most recent call last):
  File "input/code.py", line 16, in <module>
    merkki...

Test 11

Verdict: RUNTIME ERROR

Traceback (most recent call last):
  File "input/code.py", line 16, in <module>
    merkki...

Test 12

Verdict: RUNTIME ERROR

Traceback (most recent call last):
  File "input/code.py", line 16, in <module>
    merkki...

Test 13

Verdict: RUNTIME ERROR

Traceback (most recent call last):
  File "input/code.py", line 16, in <module>
    merkki...

Test 14

Verdict: RUNTIME ERROR

Traceback (most recent call last):
  File "input/code.py", line 16, in <module>
    merkki...

Test 15

Verdict: RUNTIME ERROR

Traceback (most recent call last):
  File "input/code.py", line 16, in <module>
    merkki...

Test 16

Verdict: RUNTIME ERROR

Traceback (most recent call last):
  File "input/code.py", line 16, in <module>
    merkki...