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

int n,w,dp[3][5002],e[5001],c[5001],lc,lp,i,j;
int main()
{
    fin>>n>>w;

    for(i=1;i<=n;i++)
        fin>>e[i]>>c[i];

    lc=1;
    lp=2;

    for(i=1;i<=w;i++)
        dp[lp][i]=999999;

    for(i=1;i<=n;i++)
    {


        for(j=1;j<=w;j++)
        {
            dp[lc][j]=dp[lp][j];

            if(e[i]>=j)
            {
                dp[lc][j]=min(dp[lc][j], c[i]);
            }

            else dp[lc][j]=min(dp[lc][j], dp[lp][j-e[i]]+c[i]);
        }

        swap(lc,lp);
    }
        if(dp[lp][w]==999999) fout<<-1;
        else
        fout<<dp[lp][w];
    return 0;
}