#include <fstream>
#define nmax 1002
#define kmax 5002
using namespace std;
ifstream fin("energii.in");
ofstream fout("energii.out");

int calc[nmax][kmax],sum_power=0;
int cost[nmax],power[nmax],nr_gen,needed_power;

int main()
{
    fin>>nr_gen>>needed_power;
    int ma=0;
    for(int i=1;i<=nr_gen;i++)
        for(int j=1;j<=needed_power;j++)
            calc[i][j]=1000000002;
    for(int i=1;i<=nr_gen;i++){
        fin>>power[i]>>cost[i];
        sum_power+=power[i];
        if(power[i]>ma)
            ma=power[i];
    }
    if(sum_power<needed_power)
        fout<<-1;
    else
    {
        calc[1][power[1]]=cost[1];
        for(int i=2;i<=nr_gen;i++)
        {
            for(int j=0;j<=needed_power+power[i];j++)
            {
                calc[i][j]=calc[i-1][j];
                if(j>needed_power)
                {
                    calc[i][needed_power]=min(calc[i][needed_power],min(calc[i-1][needed_power],calc[i-1][j-power[i]]+cost[i]));
                }
                if(power[i]<=j)
                {
                    calc[i][j]=min(calc[i][j],calc[i-1][j-power[i]]+cost[i]);
                }
            }
        }
        fout<<calc[nr_gen][needed_power];
    }
    return 0;
}