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;

int main(){
	long long n,m;
	cin>>n>>m;

	vector<pair<long long,long long>> pt;

	for(int i = 0; i < n; i++){
		int x,y;cin>>x>>y;
		pt.emplace_back(make_pair(x,y));
	}
	sort(pt.begin(),pt.end());
	long long int res = 0;

	for(auto &p : pt){
		if(m==0) break;
		long long mn = min(m,p.second);
		res+=(long long)(mn*p.first);
		m-=mn;
	}
	cout<<res;
}