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:
# -*- coding: utf-8 -*-
# 整数の入力
n, m = map(int, raw_input().split())

dic = {} # yen: many

for i in range(n):
    a, b = map(int, raw_input().split())
    if a in dic: dic[a] += b
    else: dic.update({a:b})

dic = sorted(dic.items())

count = 0
yen = 0
for k, v in dic:

    if v < m-count:
        yen += k*v
        count += v
    else:
        yen += k*(m-count)
        count += m-count
        print yen
        break