Python

import math

def decrypt_message(message):
    n = len(message)
    root_n = math.sqrt(n)
    rows = 0
    cols = 0

    for r in range(int(root_n), 0, -1):
        if n % r == 0:
            rows = r
            cols = n // rows
            break

    matrix = [['' for _ in range(cols)] for _ in range(rows)]
    index = 0

    for c in range(cols):
        for r in range(rows):
            matrix[r][c] = message[index]
            index += 1

    decrypted = ''
    for r in range(rows):
        for c in range(cols):
            decrypted += matrix[r][c]

    return decrypted

message = input()
print(decrypt_message(message))