#include<fstream>
using namespace std;
ifstream f("energii.in");
ofstream g("energii.out");
int n,i,w,s,ok,b[1002];
float c[1002],aux,a[1002];
int main()
{f>>n;f>>w;
for(i=1;i<=n;i++)
{f>>a[i]>>b[i];c[i]=b[i]/a[i];s=s+a[i];}
if(s<w) g<<"-1";
else {do{ok=1;
for(i=1;i<=n-1;i++)
if(c[i]>c[i+1]) {aux=a[i];a[i]=a[i+1];a[i+1]=aux;ok=0;
aux=b[i];b[i]=b[i+1];b[i+1]=aux;
aux=c[i];c[i]=c[i+1];c[i+1]=aux;}}
while(ok==0);
s=0;i=1;
while(s<w)
s=s+b[i];
g<<s;}
f.close();
g.close();
return 0;}