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
import sys

head = sys.stdin.readline()
[n, m] = head.split(" ")
n = long(n)  # 店の件数
m = long(m)  # 購入本数

amount = 0

# 店の件数分読み込み
rows = [sys.stdin.readline() for _ in range(n)]
rows.sort(key=lambda x: long(x.split(" ")[0]))
for row in rows:
    [a, b] = row.strip().split(" ")
    ai = long(a) # 金額
    bi = long(b) # 購入可能な数量
    # 購入可能な最大数まで買う
    x = bi if m >= bi else m
    for var in range(x):
        amount += ai
    m -= x
    if m == 0:
        break

print amount