#include <fstream>
using namespace std;

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

int G, E, i, j, cost, nrg;
long long s[5001];
int main() {
    fin >> G >> E;
    for (i = 1; i <= G; i++) {
    	fin >> nrg >> cost;
    	for (j = E; j > 0; --j) {
            if (s[j]) {
                if (j + nrg > E) {
                    if ((s[E] > s[j] + cost) || !s[E]) {
                        s[E] = s[j] + cost;
                    }
                }else
                    if ((s[j + nrg] > s[j] + cost) || !s[j + nrg])
                        s[j + nrg] = s[j] + cost;
            }
            if (j == nrg)
                if (!s[j]) {
                    s[j] = cost;
                }else if (s[j] > cost) {
                    s[j] = cost;
                }
    	}
    }
    fin.close();
    if (s[E])
        fout << s[E];
    else
        fout << -1;
    fout.close();
    return 0;
}