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 int long long
#define f(i,n) for(int i=0;i<n;i++)
#define F first
#define S second
#define mod 1000000007
#define P pair<int,int>
using namespace std;
P p[100000];
signed main(){
	int a,b,ans=0;
	cin>>a>>b;
	f(i,a) cin>>p[i].F>>p[i].S;
	sort(p,p+a);
	f(i,a){
		if(b<=p[i].S){
			cout<<ans+p[i].F*b<<endl;
			return 0;
		}
		ans+=p[i].F*p[i].S;
		b-=p[i].S;
	}
}