#include <fstream>

using namespace std;

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

const int N = 1001;
const int K = 5001;
const int INF=1000000000;

int cost[K],g[N],p[N];

int main()
{
    int n,k,s=0,jj;
    in>>n>>k;
    for(int i=1; i<=n; i++)
    {
        in>>g[i]>>p[i];
    }
    for(int i=1; i<=k; i++)
        cost[i]=INF;
    for(int i=1; i<=n; i++)
    {
        for(int j=k-1; j>=0; j--)
        {
            if(cost[j]!=INF)
            {
                if (j + g[i] > k)
                {
                    jj = k;
                }
                else
                {
                    jj = j + g[i];
                }
                if(cost[j] + p[i] < cost[jj])
                {
                    cost[jj] = cost[j] + p[i];
                }
            }
        }
    }
    if (cost[k] == INF)
    {
        cost[k] = -1;
    }
    out << cost[k];
    return 0;
}