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:
import sys

l = raw_input().split()
N = int(l[0])
M = int(l[1])

AB = [[0 for i in range(2)] for j in range(N)]

for n in range(N):
    l = raw_input().split()
    AB[n][0] = int(l[0])
    AB[n][1] = int(l[1])

ab = sorted(AB, key=lambda a: a[0])
#print(ab)

sum = 0
drinks = 0
for n in range(N):
    a = ab[n]
    if drinks + a[1] < M:
        sum += a[0] * a[1]
        drinks += a[1]
    else:
        num = M - drinks
        sum += a[0] * num
        drinks += num
        break

print(sum)