#include <fstream>
#include <vector>

using namespace std;

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

const int GMAX = 1005;
const int WMAX = 5005;
const int oo = 20022002;
int G, W;
vector <pair<int, int> > V;
int DP[GMAX][WMAX];

void Read(){
    in >> G >> W;
    for(int i = 1; i <= G; ++i){
        int energy, cost;
        in >> energy >> cost;
        V.push_back(make_pair(energy, cost));
    }
    for(int i = 0; i <= W; ++i)
        DP[0][i] = oo;
}

void SolveAndPrint(){
    for(int i = 1; i <= G; ++i){
        for(int energy = 1; energy <= W; ++energy){
            int generator_energy = V[i - 1].first;
            int generator_cost = V[i - 1].second;
            DP[i][energy] = DP[i - 1][energy];
            if(generator_energy >= energy)
                DP[i][energy] = min(DP[i][energy], generator_cost);
            else
                DP[i][energy] = min(DP[i][energy], generator_cost 
                    + DP[i - 1][energy - generator_energy]);
        }
    }
    out << (DP[G][W] != oo ? DP[G][W] : -1) << "\n";
}

int main(){
    Read();
    SolveAndPrint();
}