#include<fstream>
using namespace std;
ifstream f("energii.in");
ofstream h("energii.out");
int a[9999],b[9999],w,inv,g,i,j,minn,n,ok,aux,s;
int main (){
	f>>g>>w;
	for(i=1;i<=g;i++){
		f>>a[i];
		f>>b[i];}
	do{inv=0;
	for(i=1;i<g;i++){
		if(b[i]<b[i+1]){
			aux=b[i];
			b[i]=b[i+1];
			b[i+1]=aux;
			aux=a[i];
			a[i]=a[i+1];
			a[i+1]=aux;
			inv=1;}}
	}while(inv==1);
	for(i=1;i<=g && ok==0;i++){
		if(s>=w)
			ok=1;
		else
			s+=b[i];}
	if(s<w && i>n)
		h<<-1;
	else
		h<<s;
	return 0;
}