#include<cstdio>
#include<algorithm>
using namespace std;
struct gen
{
	int e,c;
}v[1001];
bool comp(gen a,gen b)
{
	return (float)a.e/a.c>(float)b.e/b.c;
}
int main()
{
	freopen("energii.in","r",stdin);freopen("energii.out","w",stdout);
	int g,w,i,s1=0,s2=0;
	scanf("%d%d",&g,&w);
	for(i=1;i<=g;++i)
		scanf("%d%d",&v[i].e,&v[i].c);
	sort(v+1,v+g+1,comp);
	for(i=1;i<=g&&s1<w;++i)
		s1+=v[i].e,s2+=v[i].c;
	if(i==g+1&&s1<w)
		printf("-1");
	else
		printf("%d",s2);
}