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 LL long long

int main()
{
  LL n,m,j=0,ans=0;
  pair<LL,LL> pii[100005];

  cin>>n>>m;

  for(int i=0; i<n; i++){
    cin>>pii[i].first>>pii[i].second;
  }

  sort(pii,pii+n);

  while(m>0){
    if(m>=pii[j].second){
      ans+=pii[j].second*pii[j].first;
      m-=pii[j].second;
      j++;
    }else{
      ans+=pii[j].first*m;
      m=0;
    }
  }
  cout<<ans<<'\n';
  return 0;
}