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>
#define rep(i, n) for (int i = 0; i < (n); i++)
using namespace std;

int main() {
	int n, m;
	long long sum = 0;
	cin >> n >> m;
	vector<pair<int, int>> dr(n);

	rep(i, n) {
		int ai, bi;
		cin >> ai >> bi;
		dr[i] = make_pair(ai, bi);
	}
	sort(dr.begin(), dr.end());
	int j = 0;
	rep(i, m) {
		sum += dr[j].first;
		dr[j].second--;
		if (dr[j].second == 0) {
			j++;
		}
	}
	cout << sum << endl;
	return 0;
}