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