def convert_case(text):
    return text.swapcase()

def main():
    with open('data.txt', 'r') as file:
        data = file.read()

    converted_data = convert_case(data)

    with open('output.txt', 'w') as file:
        file.write(converted_data)

    print("Регистр букв изменён. Результат записан в output.txt")

if __name__ == "__main__":
    main()