Problem: Hearing that energy drinks increase rating in those sites, Takahashi decides to buy up M cans of energy drinks.

There are N stores that sell energy drinks. In the i-th store, he can buy at most B_i cans of energy drinks for A_i yen (the currency of Japan) each.

What is the minimum amount of money with which he can buy M cans of energy drinks?

It is guaranteed that, in the given inputs, a sufficient amount of money can always buy M cans of energy drinks.

Constraints

* All values in input are integers.
* 1 \leq N, M \leq 10^5
* 1 \leq A_i \leq 10^9
* 1 \leq B_i \leq 10^5
* B_1 + ... + B_N \geq M

Input

Input is given from Standard Input in the following format:


N M
A_1 B_1
A_2 B_2
\vdots
A_N B_N


Output

Print the minimum amount of money with which Takahashi can buy M cans of energy drinks.

Examples

Input

2 5
4 9
2 4


Output

12


Input

4 30
6 18
2 5
3 10
7 9


Output

130


Input

1 100000
1000000000 100000


Output

100000000000000

Solution (in PYTHON):

Solution:
from operator import itemgetter

N_shop, M_required_drink  = map(int, raw_input().split())

shop_list = []
for tmp_shop in range(N_shop):
  shop_list.append(map(int, raw_input().split()))

total_money = 0
got_drink = 0
for i in sorted(shop_list, key=itemgetter(0)):
  limit_at_shop = i[1]
#  print(i)

  while got_drink < M_required_drink and limit_at_shop > 0:
    total_money = total_money + i[0]
    got_drink   = got_drink + 1
    limit_at_shop = limit_at_shop - 1
#    print("  %s %s %s" % (total_money, got_drink, limit_at_shop))

print(total_money)