#include<bits/stdc++.h>
using namespace std;
const int NMAX = 500+1;
//pair<int, int> tempsNec[NMAX];
pair<int, int> tempsNecA[NMAX];
int nbVilles, nbNec;
const int INFINI = 10000000;
struct pourNecB {
int valA, valB, iVille;
bool operator<(const pourNecB &other) const {
if(valB < other.valB)
{
return true;
}
if(other.valB < valB) return false;
return valA > other.valA;
}
};
pourNecB tempsNecB[NMAX];
/*
double dejaVu[NMAX][NMAX][NMAX];
double tempsMin(int iVille, int nbPris, int nbCollab)
{
if(nbPris >= nbNec)
{
return 0;
}
if(iVille >= nbVilles)
{
return INFINI;
}
double nbACollab = nbCollab;
double A = tempsNec[iVille].first;
double B = tempsNec[iVille].second;
double opt1 = tempsMin(iVille+1, nbPris, nbCollab);
double opt2 = tempsMin(iVille+1, nbPris+1, nbCollab) + A/nbACollab;
double opt3 = tempsMin(iVille+1, nbPris+1, nbCollab+1) + B/nbACollab;
if(B == -1)
{
opt3 = INFINI;
}
cout << iVille << " " << nbPris << " " << nbCollab << " : " << min(min(opt1, opt2), opt3) << endl;
return dejaVu[iVille][nbPris][nbCollab] = min(min(opt1, opt2), opt3);
}
/** */
bool vuCollab[NMAX];
int main()
{
ios::sync_with_stdio(false);
cin.tie(0);
cin >> nbVilles >> nbNec;
for(int i = 0; i < nbVilles; i++)
{
int a, b;
cin >> a >> b;
if(b == -1) b = INFINI;
// tempsNec[i] = {a, b};
tempsNecA[i] = {a, i};
tempsNecB[i] = {a, b, i};
}
sort(tempsNecA, tempsNecA+nbVilles);
sort(tempsNecB, tempsNecB+nbVilles);
/*/
for(int i = 0; i < nbVilles; i++)
{
cout << tempsNecA[i].first << " " << tempsNecA[i].second << endl;
}
cout << endl;
for(int i = 0; i < nbVilles; i++)
{
cout << tempsNecB[i].valA << " " << tempsNecB[i].valB << " " << tempsNecB[i].iVille << endl;
}
/**/
double meillCoup = 0;
double coupActu = 0;
double ancCoupCollab = 0;
for(int i = 0; i < nbNec; i++) meillCoup += tempsNecA[i].first;
for(int nbCollabPlus = 0; nbCollabPlus < nbVilles; nbCollabPlus++)
{
// cout << nbCollabPlus << endl;
double nbCollaborateurs = nbCollabPlus+1;
coupActu = ancCoupCollab;
double valCollab = tempsNecB[nbCollabPlus].valB;
if(valCollab == INFINI) break;
coupActu += valCollab/nbCollaborateurs;
nbCollaborateurs += 1;
vuCollab[tempsNecB[nbCollabPlus].iVille] = true;
int nbVillesAVoir = nbNec-nbCollabPlus-1;
int iVilleA = 0;
ancCoupCollab = coupActu;
while(nbVillesAVoir > 0)
{
while(vuCollab[tempsNecA[iVilleA].second])
{
iVilleA++;
}
double valA = tempsNecA[iVilleA].first;
coupActu += valA/nbCollaborateurs;
nbVillesAVoir--;
iVilleA++;
}
meillCoup = min(meillCoup, coupActu);
}
cout << meillCoup;
// cout << tempsMin(0, 0, 1);
}
