题目描述
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
输入格式
见题面
输出格式
见题面