#include<fstream.h>
 ifstream f("energii.in");
 ofstream g("energii.out");
    int main(){
		double v[10001],max;
		long ok=0,poz,i,n,ene,x,y,bani=0,a1[10001],a2[10001],enei;
		f>>n>>ene;
		for(i=1;i<=n;++i){
			f>>a1[i]>>a2[i];
			v[i]=(double)a1[i]/a2[i];
			//g<<a1[i]<<' '<<a2[i]<<'\n';
		}
		//g<<v[1]<<' '<<v[2]<<' '<<v[3];
		while(ene){
			max=0;
			enei=ene;
			for(i=1;i<=n;++i){
				if(max<v[i] && v[i]<ene && v[i]){
					max=v[i];
					poz=i;
					x=a1[i];
					y=a2[i];
				}
				else
				if(v[i]>ene) v[i]=0;
			}
			if(max){
			    while(max<ene && ene){
				    ene-=x;
				    bani+=y;
			    }
			}
			else
				ene=0;
			v[poz]=0;
			//ok++;
		}
		g<<bani<<"\n";
		return 0;
	}