#include <iostream>
#include <fstream>
#define L_MAX 100000
using namespace std;
ifstream f("rucsac.in");
ofstream g("rucsac.out");
int gr[L_MAX], val[L_MAX];
double v[L_MAX];
int main()
{
    int n, m, i, y, x, j, s=0, z;
    f>>n>>m;
    for(i=1; i<=n; i++)
        {f>>gr[i]>>val[i];
        v[i]=(double)val[i]/gr[i];}
    for(i=2; i<=n; i++)
    {
        x=v[i]; y=gr[i]; z=val[i];
        j=i-1;
        while(j>=1 && v[j]<x)
        {v[j+1]=v[j];
            j--;
        }
            val[j+1]=z; gr[j+1]=y; v[j+1]=x;
    }
    for(i=n; i>=1; i--)
        if(gr[i]<m && m>=0)
    {
        s=s+val[i];
        m=m-gr[i];
    }
    g<<s;
    return 0;
}