#include <iostream>
#include <stdio.h>
#include<algorithm>
using namespace std;
FILE *in,*out;
int n,gmax;
long long ct=0;
struct obiect
{
    int g;int v;
}r[5001];
bool cmp( obiect a,obiect b)
{
    return(a.v * b.g> a.g * b.v);
}
int main()
{   in=fopen("rucsac.in","r");
    out=fopen("rucsac.out","w");
    int i;
    fscanf(in,"%d %d",&n,&gmax);
    for(i=1;i<=n;i++)
        fscanf(in,"%d %d",&r[i].g,&r[i].v);
    sort(r+1,r+n+1,cmp);
    for(i=1;i<=n && gmax>0 ;i++)
    {
        if(r[i].g<=gmax)
        {
            gmax-=r[i].g;
            ct+=r[i].v;
        }
    }
    fprintf(out,"%lld",ct);
    return 0;
}