#include <cstdio>
using namespace std;
FILE *f, *g;
int i,j,k,ep,c,n,b[5002];
int main()
{f=fopen ("energii.in","r");
g=fopen ("energii.out","w");
fscanf (f,"%d%d",&n,&k);
for(i=1;i<=k;++i)
b[i]=999999999;
for(i=1;i<=n;++i)
{fscanf (f,"%d%d",&ep,&c);
for(j=k;j>=ep;--j)
if(b[j]>b[j-ep]+c)
b[j]=b[j-ep]+c;
for(j=ep;j>=1;--j)
if(b[j]>c)
b[j]=c;
}
if(b[k]!=999999999)
fprintf (g,"%d\n",b[k]);
else
fprintf (g,"-1\n");
return 0;
}