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.

Input is given from Standard Input in the following format:

```
$N$ $M$
$A_1$ $B_1$
$A_2$ $B_2$
$\vdots$
$A_N$ $B_N$
```

Print the minimum amount of money with which Takahashi can buy $M$ cans of energy drinks.

-   All values in input are integers.
-   $1 \leq N, M \leq 10^5$
-   $1 \leq A_i \leq 10^9$
-   $1 \leq B_i \leq 10^5$
-   $B_1 + ... + B_N \geq M$

12

With 12 yen, we can buy one drink at the first store and four drinks at the second store, for the total of five drinks. However, we cannot buy 5 drinks with 11 yen or less.