//#define _GLIBCXX_DEBUG
#include <bits/stdc++.h>
#define int long long
#define ld long double
using namespace std;
const int INF = 1e18;
const int mod = 1e9+7;
ld cost(int cnt_users,vector <pair<int,int>> &free,int need) {
ld ans = 0;
sort(free.begin(),free.end());
for (int i = 0;i < need;i++) {
ans += free[i].first / (cnt_users * 1.0l);
}
return ans;
}
signed main() {
mt19937 rng(69);
int n,k;
cin >> n >> k;
vector <pair<int,int>> vec(n);
vector <pair<int,int>> govno,good;
for (int i = 0;i < n;i++) {
cin >> vec[i].first >> vec[i].second;
if (vec[i].second == -1) {
govno.push_back(vec[i]);
}else {
good.push_back(vec[i]);
}
}
sort(good.begin(),good.end(),[&] (pair<int,int> a,pair<int,int> b) {
return a.second < b.second;
});
ld best = INF;
for (int cnt_support = 0;cnt_support <= good.size();cnt_support++) {
vector <pair<int,int>> tmp;
for (auto el : govno) {
tmp.push_back(el);
}
ld ans = 0;
for (int i = 0;i < cnt_support;i++) {
ans += (good[i].second) / ((1 + i) * 1.0l);
}
for (int i = cnt_support;i < good.size();i++) {
tmp.push_back(good[i]);
}
ans += cost(cnt_support + 1,tmp,max(0ll,k - cnt_support));
best = min(best,ans);
}
cout << fixed << setprecision(15) << best << "\n";
}
