#include <fstream>
#include <set>

#define INF 20001000
using namespace std;

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

int costM[5005];

int main()
{
    int n, need;
    fin >> n >> need;

    for(int i = 1; i <= need; ++i)
        costM[i] = INF;

    for(int i = 1; i <= n; ++i)
    {
        int cant, cost;
        fin >> cant >> cost;

        for(int j = need; j >= 0; --j)
            costM[min(j + cant, need)] = min(costM[min(j + cant, need)], costM[j] + cost);
    }

    if(costM[need] == INF)
        fout << -1 << '\n';
    else fout << costM[need] << '\n';
    return 0;
}