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;
#define FOR(x,to) for(x=0;x<(to);x++)

int main()
{
    long int n,m,i;cin>>n>>m;
    vector<pair<long int,long int>> ab(n);
    FOR(i,n){cin >> ab[i].first>>ab[i].second;}
    sort(ab.begin(),ab.end());
    long int ans=0,res=m,k=0;
    while (res>0) {
        ans+=ab[k].first*min(res,ab[k].second);
        res-=ab[k].second;
        k++;
    }
    cout<<ans<<endl;

}