#include<stdio.h>
int main(){
	int g,w,v1[1000],v2[1000],j,i,s,c,a;
	freopen("energii.in","r",stdin);
	freopen("energii.out","w",stdout);
	scanf("%d",&g,&w);
	for (i=0;i<g;++i)
		scanf("%d%d",&v1[i],&v2[i]);
	for (i=0;i<g-1;++i)
		for (j=i+1;j<g;++j)
			if (v2[i]>v2[j]){
				a=v2[i];
				v2[i]=v2[j];
				v2[j]=a;
				a=v1[i];
				v1[i]=v1[j];
				v1[j]=a;
			}
	i=0;s=0;c=0;
	while ((s<w)&&(i<g)){
		s+=v2[i];
		c+=c+v1[i];
		i+=1;
	}
	if (s<w) printf("-1\n");
	else printf("%d",c);
	return 0;
}