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>
typedef long long ll;

using namespace std;

int main() {
	ll n, m;
	cin >> n >> m;
	
	multimap<ll, ll> mapping;
	
	for(ll i=0; i < n; i++) {
		ll cost, cnt;
		cin >> cost >> cnt;
		mapping.insert({cost, cnt});
	}
	
	ll total_cost = 0;
	for(auto& p : mapping) {
		ll cnt = min(m, p.second);
		m -= cnt;
		total_cost += cnt * p.first;
		
		if(m == 0) break;
	}
	
	cout << total_cost;
	
	return 0;
}