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; 
struct ener{
	long long x;
	long long y;
}a[100005];
bool cmp(ener a,ener b)
{
    return a.x<b.x;
}
long long n,m,ans,sum;
int main(){
    cin>>n>>m;
    for(int i=1;i<=n;i++)
        cin>>a[i].x>>a[i].y;
    sort(a+1,a+1+n,cmp);
    for(int i=1;i<=n;i++)
    { 
    	if(a[i].y+sum>=m) {ans+=(m-sum)*a[i].x;break;}
    	else ans+=a[i].x*a[i].y,sum+=a[i].y;
	}
	cout<<ans;
	return 0;
}