#include<iostream>
#include<algorithm>
using namespace std;
struct milk
{
	int price;
	int amount;
};
milk m[500009];
bool cmp(milk x,milk y)
{
	return x.price < y.price;
}

int main()
{
	int n,s,p=0;
	cin >> n >> s;
	for(int i=0;i<n;i++)
	{
		cin >> m[i].price >> m[i].amount;
	}
	sort(m,m+n,cmp);
	for(int i = 0;i < n;i++) 
	{
		if(n-m[i].amount >= 0)
		{
			p+=m[i].price * m[i].amount;
			n-=m[i].amount;
		} 
		else
		{
			p+=n*m[i].price;
			break;
		}
	} 
	cout << p <<endl;
    return 0;	
} 

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