def stock_increase(dic, code, size, color, n):
    t = (code,size,color)
    if t in dic:
        dic[t] = dic[t] + n
    else:
        dic[t] = n

def stock_decrease(dic, code, size, color, n):
    t = (code,size,color)
    dic[t] = dic[t] - n

def low_stock(dic,n):
    l = []
    for p in dic:
        if dic[p] < n:
            l.append(p)
    return l

def update_stock(dic,lsale,lrestock):
    for sale in lsale:
        stock_decrease(dic,sale[0],sale[1],sale[2],sale[3])
    for p in lrestock:
        stock_increase(dic,p[0],p[1],p[2],p[3])