import datetime

def get_last_friday(date_string):
    parts = date_string.split("/")
    mounth = int(части[0])
    year = int(части[1])
    if mounth == 12:
        first = datetime.data(year +1,1,1)
    else:
        first = datetime.date(year,mounth+1,1)
last = first - datetime.timedelta(days=1)
now = last
    while True:
        if now.isoweekday() ==5:
            break
        else:
            now = now - datetime.timedelta(days=1)
    result = now.strftime("%d.%m.%Y")
    return result