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 int
#define oo 987654321
using namespace std;
INT n, m, ans, i;
pair<INT, INT> x[100010];

int main()
{
    ios::sync_with_stdio(false);
    cin>>n>>m;
    for(int i = 0 ; i < n ; i++ ) cin>>x[i].first>>x[i].second;
    sort(x, x+n);
    while( m-- )
    {
        if( x[i].second == 0 ) i++;
        ans += x[i].first, x[i].second--;
    }
    cout<<ans<<endl;
    return 0;
}