#include <fstream>
using namespace std;

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

const int INF = 0x3f3f3f3f;
int g, w, ce, cn;
int c[5005];

int main()
{
    fin >> g >> w;
    for ( int i = 1; i <= w; i++ )
        c[i] = INF;
    for ( ; g; g-- )
    {
        fin >> ce >> cn;
        for ( int i = w - ce; i >= 0; i-- )
            if ( c[i] < INF )
                if ( c[i + ce] > c[i] + cn )
                    c[i + ce] = cn + c[i];
    }
    if ( c[w] == INF )
        fout << "-1\n";
    else
        fout << c[w] << '\n';
    fin.close();
    fout.close();
    return 0;
}