def writeTextToFile(parametr):
    with open('soubor.log', mode='w', encoding='utf-8') as file:
        file.write(zreteny)
    zreteny = STATICKY_TEXT + str(parametr)
    print(zreteny)
    return

STATICKY_TEXT = "This is my static text which must be added to file. It is very long text and I do not know what they want to do with this terrible text."
parametr = input("Zadej parametr: ")