#include<fstream>
using namespace std;

#define nmax 1002

int w[nmax],c[nmax],n,m,a[nmax][5002];

int mini(int b, int d)
{
	if(b<d) return b;
	else return d;
}




int main()
{
	ifstream f("energii.in");
	ofstream g("energii.out");
	
	f>>n>>m;
	
	for(int i=1;i<=n;i++)
		f>>w[i]>>c[i];
	
	for(int i=1;i<=n;i++)
		for(int j=1;j<=m;j++)
		{
			if(i==1)
			{
				if(j%w[i]==0)
				a[i][j]=(j/w[i])*c[i];
				else
					a[i][j]=((j/w[i])+1)*c[i];
				continue;
			}
			
			if(j%w[i]==0)
				a[i][j]=mini(a[i-1][j],(j/w[i])*c[i]);
			else
				a[i][j]=mini(a[i-1][j],((j/w[i])+1)*c[i]);
		}
		
	g<<a[n][m];
}