#include <bits/stdc++.h>
#define int long long
using namespace std;
#define sz(v) ((int)(v).size())
#define all(v) (v).begin(), (v).end()
#define L(i, j, k) for(int i = (j); i <= (k); ++i)
#define R(i, j, k) for(int i = (j); i >= (k); --i)
#define double long double
std::mt19937 rng(std::chrono::steady_clock::now().time_since_epoch().count());
const int mod=1e9;
void solve() {
int n,k;cin>>n>>k;
vector<pair<int,int>> vec(n);
L(i,0,n-1)cin>>vec[i].first>>vec[i].second;
sort(all(vec));
vector<int> ord;
L(i,0,n-1){
if(vec[i].second!=-1){
ord.push_back(i);
}
}
sort(all(ord),[&](int a,int b){
return vec[a].second<vec[b].second;
});
double resp=mod;
vector<bool> usei(n,0);
L(i,0,sz(ord)){//usando quantos falantes
int qnt=i+1;
double respat=0;
L(j,0,i-1){
usei[ord[j]]=1;
respat+=(double)vec[ord[j]].second/(j+1);
}
int id=0;
int quero=k-i;
while(quero>0){
if(usei[id]){
id++;continue;
}
respat+=(double)vec[id].first/qnt;
quero--;
id++;
}
resp=min(resp,respat);
}
cout<<setprecision(11);
cout<<resp;
}
int32_t main() {
std::cin.tie(0)->sync_with_stdio(0);
std::cin.exceptions(std::cin.failbit);
int T = 1;
// std::cin >> T;
while(T--) {
solve();
}
return 0;
}
