#include <fstream>
using namespace std;
ifstream f("energii.in");
ofstream g("energii.out");
int n,s,i,x,y,j,v[5002];
int main()
{
    f>>n>>s;
    for(i=1;i<=s;i++)
        v[i]=5006002;
    for(i=1;i<=n;i++)
    {
        f>>x>>y;
        for(j=0;j+x<=s;j++)
            if(v[j]!=5006002)
                v[j+x]=min(v[j+x],v[j]+y);
    }
    if(v[s]!=5006002)
        g<<v[s];
        else
            g<<-1;
    return 0;
}