#include <fstream>
#include <algorithm>
using namespace std;
ifstream fin("pr.in");
ofstream fout("pr.out");
struct rucsac{int g,p;
            float r;};
rucsac v[1000];
bool comp(rucsac a,rucsac b)
{
    return(a.r>b.r);

}
int main()
{int n,i,S,G;
    fin>>n>>G;
    for(i=1;i<=n;i++)
    {
        fin>>v[i].g>>v[i].p;
        v[i].r=(float)v[i].p/v[i].g;


    }
    S=0;
    for(i=1;i<=n&&G>0;i++)
        if(v[i].g<=G)
    {
        G=G-v[i].g;
        S=S+v[i].p;

    }
    fout<<S;

    return 0;
}