from datetime import datetime, timedelta

def get_last_friday(a: str) -> str:
    date = datetime.strptime(a, "%m/%Y").date()
    next_month = date.replace(day=28) + timedelta(days=7)
    last_day = next_month - timedelta(days=next_month.day)
    
    # Идем назад до пятницы
    while last_day.weekday() != 4:
        last_day -= timedelta(days=1)
    
    return last_day.strftime("%d.%m.%Y")