#include<stdio.h>
#include<stdlib.h>
#include<string.h>
struct gen{
	int e,c;
};
int comp(const void*a,const void*b){
	gen *aa=(gen*)a,*bb=(gen*)b;
	gen x=*aa,y=*bb;
	if((double)x.c/x.e>(double)y.c/y.e)
		return 1;
	if((double)x.c/x.e<(double)y.c/y.e)
		return -1;
	return 0;
}
int main(){
	FILE*in=fopen("energii.in","r");
	FILE*out=fopen("energii.out","w");
	int g,w,i,s=0,cost=0;
	gen x[1001];
	fscanf(in,"%d %d",&g,&w);
	for(i=0;i<g;i++)
		fscanf(in,"%d %d",&x[i].e,&x[i].c);
	qsort(x,g,sizeof(x[0]),comp);
	
	i=0;
	while((s<w)&&(i<g)){
		s=s+x[i].e;
		cost=cost+x[i].c;
		i++;
	}
	if(s<w)
		fprintf(out,"-1\n");
	if(s>=w)
		fprintf(out,"%d\n",cost);
	fclose(in);
	fclose(out);
	return 0;
}