Ошибка "TypeError: can only concatenate str (not "int") to str"

import random
import string
 
def numberstring(num):
    sample = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyzАБВГДЕЁЖЗИЙКЛМНОПРСТУФХЦЧШЩЪЫЬЭЮЯабвгдеёжзийклмнопрстуфхцчшщъыьэюя'
    res = ''.join((random.choice(sample)) for i in range(num))
    print("generated string:", res)
    listed = list(res)
    syllable = int(2)
    counter = syllable
    for j in res:
        if counter % syllable > 0 and syllable % 2 == 0:
            listed[j], listed[j+1] = listed[j+1], listed[j]
            ''.join(listed)
        if counter % syllable > 0 and syllable % 3 == 0:
            listed[j], listed[j+1], listed[j+2] = listed[j+2], listed[j+1], listed[j]
            ''.join(listed)
        if counter % syllable > 0 and syllable % 4 == 0:
            listed[j], listed[j+1], listed[j+2], listed[j+3] = listed[j+3], listed[j+2], listed[j+1], listed[j]
            ''.join(listed)
        counter+=1
    print("changed string:", res)
    
print("How many symbols do you want to see in the string?")
num = int(input())
numberstring(num)

>>> '1'+1
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: can only concatenate str (not "int") to str

import random
import string
 
 
def numberstring(num):
    sample = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyzАБВГДЕЁЖЗИЙКЛМНОПРСТУФХЦЧШЩЪЫЬЭЮЯабвгдеёжзийклмнопрстуфхцчшщъыьэюя'
    res = ''.join((random.choice(sample)) for i in range(num))
    print("generated string:", res)
    listed = list(res)
    syllable = int(2)
    counter = syllable
    for j in range(len(res)-3):
        if counter % syllable > 0 and syllable % 2 == 0:
            listed[j], listed[j + 1] = listed[j + 1], listed[j]
            res = ''.join(listed)
        if counter % syllable > 0 and syllable % 3 == 0:
            listed[j], listed[j + 1], listed[j + 2] = listed[j + 2], listed[j + 1], listed[j]
            res = ''.join(listed)
        if counter % syllable > 0 and syllable % 4 == 0:
            listed[j], listed[j + 1], listed[j + 2], listed[j + 3] = listed[j + 3], listed[j + 2], listed[j + 1], \
                                                                     listed[j]
            res = ''.join(listed)
        counter += 1
    print("changed string:", res)
 
 
print("How many symbols do you want to see in the string?")
num = int(input())
numberstring(num)