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 >>a(n);
for(long long  i=0;i<n;i++){
    long long  aa,aaa;
    cin >> aa >>aaa;
    a.at(i)=make_pair(aa,aaa);
}
sort(a.begin(),a.end());
long long j=0;
long long che=0;
for(long long  i=0;i<m;i++){
if(a.at(j).second==0)j++;
    a.at(j).second--;
    che+=a.at(j).first;
}
cout <<che <<endl;
}