import datetime

if __name__ == '__main__':
    first = list(map(int, input().split(":")))
    second = list(map(int, input().split(":")))

    first_timestamp = datetime.timedelta(hours=first[0], minutes=first[1])
    second_timestamp = datetime.timedelta(hours=second[0], minutes=second[1])

    res = (first_timestamp + second_timestamp).total_seconds() % (24 * 60 * 60)


    print(f"{int(res / 60 / 60):02}:{int((res % (60*60)) / 60):02}")