#include <fstream>

using namespace std;

ifstream fin("energii.in");
ofstream fout("energii.out");

int n,en,i,j,e[1002],c[1002],d[55500],s;

int main()
{
    fin >> n >> en;
    for (i=1;i<=n;i++)
    {
        fin >> e[i] >> c[i];
        s+=e[i];
    }
    if (s<en)
    {
        fout << -1;
        return 0;
    }
    for (i=1;i<=en;i++) d[i]=55500;
    for (i=1;i<=n;i++)
    {
        for (j=en;j-e[i]>=0;j--) d[j]=min(d[j-e[i]]+c[i],d[j]);
        for (j=1;j<e[i];j++) d[j]=min(d[j],c[i]);
    }
    fout << d[en];

    return 0;
}