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:
#!/usr/bin/env python2
"""
This file is part of https://github.com/cheran-senthil/PyRival
Copyright 2019 Cheran Senthilkumar <hello@cheran.io>

"""
from __future__ import division, print_function

import itertools
import os
import sys
from atexit import register
from io import BytesIO


class dict(dict):
    """ dict() -> new empty dictionary """

    def items(self):
        """ D.items() -> a set-like object providing a view on D's items """
        return dict.iteritems(self)

    def keys(self):
        """ D.keys() -> a set-like object providing a view on D's keys """
        return dict.iterkeys(self)

    def values(self):
        """ D.values() -> an object providing a view on D's values """
        return dict.itervalues(self)


def gcd(x, y):
    """ greatest common divisor of x and y """
    while y:
        x, y = y, x % y
    return x


range = xrange

filter = itertools.ifilter
map = itertools.imap
zip = itertools.izip

sys.stdin = BytesIO(os.read(0, os.fstat(0).st_size))
sys.stdout = BytesIO()
register(lambda: os.write(1, sys.stdout.getvalue()))

input = lambda: sys.stdin.readline().rstrip('\r\n')


def main():
    n, m = map(int, input().split())
    a = [(0, 0) for _ in range(n)]

    for i in range(n):
        a[i] = tuple(map(int, input().split()))

    a.sort()
    cost = 0
    for ai in a:
        if ai[1] < m:
            cost += ai[1] * ai[0]
            m -= ai[1]
        else:
            cost += ai[0] * m
            break

    print(cost)


if __name__ == '__main__':
    main()