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