#include <stdio.h>

using namespace std;
FILE *f=fopen("energii.in","r");
FILE *g=fopen("energii.out","w");
int main()
{
    int G,W,v[100],p[100],e,c,s1,s;
    fscanf(f,"%d%d",&G,&W); s=0;
    for (int i=1;i<=G;i++)
    {
        fscanf(f,"%d%d",&v[i],&p[i]);
    }
    e=v[1]; c=p[1]; s1=0;
    while ((s1<W)||(G!=0))
{
    for (int i2=1;i2<=G;i2++)
    {
        if (v[i2]>e) {
            e=v[i2]; c=p[i2];}
        if ((v[i2]==e)&&(p[i2]<c))
        {
            e=v[i2];
            c=p[i2];
        }

    }
    s=s+c; s1=s1+e;
    if (s1>=W) break;
   G--;
   e=v[1]; c=p[1];
}
if (s1>=W) fprintf(g,"%d",s);
 else if (s1<W) fprintf(g,"%d",-1);
    return 0;
}