#include <cstdio>
using namespace std;
FILE *f, *g;
int ma,i,j,k,n,ep[5001],c[5001],b[5001];
int main()
{f=fopen ("energii.in","r");
g=fopen ("energii.out","w");
fscanf (f,"%d%d",&n,&k);
for (i=1;i<=n;++i)
fscanf (f,"%d%d",&ep[i],&c[i]);
for (i=1;i<=k;++i)
b[i]=99999999;
for (i=1;i<=n;++i)
{for (j=k;j>=ep[i];--j)
if (b[j]>b[j-ep[i]]+c[i])
b[j]=b[j-ep[i]]+c[i];
for (j=c[i];j>=1;--j)
if (b[j]>c[i])
b[j]=c[i];
}
if (b[k]!=99999999)
fprintf (g,"%d\n",b[k]);
else
fprintf (g,"-1\n");
return 0;
}