#include <iostream>
#include <fstream>
#include <algorithm>
using namespace std;

ifstream f("rucsac.in");
ofstream g("rucsac.out");

struct obj{double p,g,rap;}o[5005];
int n,k;
int d[10000][5005];
inline bool cmp(obj x,obj y){
  return x.rap<y.rap;
}
void cit(){
  f>>n>>k;
  for(int i=1;i<=n;i++){
    f>>o[i].g>>o[i].p;
    o[i].rap=o[i].g/o[i].p;
  }
}


int main()
{
    cit();
    sort(o+1,o+n+1,cmp);
    bool ok = true;
    int i=1, pr=0;
    while(ok){
      if(k<o[i].g){
        ok=false;
      }
      else{
        k-=o[i].g;
        pr+=o[i].p;
        i++;
      }
    }
    g<<pr;
/*
    for(int i=1;i<=n;i++)
      g<<o[i].p<<" "<<o[i].g<<" "<<o[i].rap<<'\n';
*/


    return 0;
}