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 CPP):

Solution:
#include <bits/stdc++.h>
using namespace std;

typedef long long LL;

int main()
{
	int N, M;
	cin >> N >> M;
	vector<pair<LL,LL>> AB(N);
	for (int i = 0; i < N; ++i) {
		cin >> AB[i].first >> AB[i].second;
	}

	sort(AB.begin(), AB.end());

	LL ans = 0;
	LL cnt = 0;
	int i = 0;
	while(cnt < M) {
		cnt += AB[i].second;
		ans += AB[i].first * AB[i].second;
		++i;
	}

	--i;
	
	ans -= AB[i].first * (cnt - M);

	cout << ans << endl;
}