#include <stdio.h>
FILE*f=fopen("energii.in","r");
FILE*g=fopen("energii.out","w");
long gj,w,max,max2,r,sav,v[1002],v2[1002],x,y,dif,i,j;
int main()
{
	fscanf(f,"%ld%ld",&gj,&w);
	max=-9999999;
	for (i=1;i<=gj;i++)
	{
		fscanf (f,"%ld%ld",&x,&y);
		v[i]=x;
		v2[i]=y;
		if (x-y>max)
			max=x-y;
	}
	for (i=1;i<=gj;i++)
		if (v[i]-v2[i]==max && v[i]>max2)
		{
			sav=v2[i];
			max2=v[i];
		}
	r=sav*w/max2;
	if (w%max2!=0)
		r=r+sav;
	fprintf(g,"%ld",r);
	fclose(f);
	return 0;
}