쇼핑몰

klist = []
inc = 0
def checkEnd(l):
    cnt = 0
    for i in range(len(l)):
        if(l[i][1] == 0):
           cnt += 1
    return cnt

def pay(l):
    for i in range(len(l)):
        if l[i][1] > 0:
            l[i] = [l[i][0], l[i][1]-1]
    return l

def exit(l):
    global inc
    sum = 0
    print(l)
    for i in range(-1, (len(l) + 1) * -1, -1): # 제일 뒤에서부터 나간다.
        if(l[i][1] == 0):
            inc += 1
            sum += l[i][0] * inc

            print("inc:", inc, ", num:" , l[i][0], ", sum:", sum)
    return sum

def addList(l):
    global klist
    newList = []
    for i in range(len(l)):
        if l[i][1] == 0:
            if len(klist) > 0:
                newList.append(klist.pop(0))
        else:
            newList.append(l[i])
    return newList


def shoppingmall():
    global klist
    sum = 0
    temp = input()

    try:
        n = int(temp.split(' ')[0])
    except:
        print("n is not integer")
        return
    try:
        k = int(temp.split(' ')[1])
    except:
        print("k is not integer")
        return
    #print(n, k)

    l = []
    for i in range(n):
        temp = input()
        klist.append([int(temp.split(' ')[0]),int(temp.split(' ')[1])])

    for i in range(k):
        l.append(klist.pop(0))


    while l:
        if checkEnd(l) > 0:
            sum += exit(l)
            l = addList(l)
        l = pay(l)

    #print(l)
    return sum
'''
10 3
123 4
21 5
34 14
56 1
45 7
723 5
55 7
13 5
910 10
73 3
'''
print(shoppingmall())