#include <iostream>
#include <iomanip>
#include <vector>
#include <cmath>
#include <algorithm>
#include <set>
#include <queue>
#include <map>
#include <unordered_map>
#include <stack>
#include <bitset>
#include <string>
#include <cstring>
#include <iterator>
#include <random>
#define ll long long
#define ld long double
#define inf (ll)(2*1e18)
#define sort(a) sort(a.begin(), a.end())
#define reverse(a) reverse(a.begin(), a.end())
#define pb push_back
#define endl "\n"
using namespace std;
void solve(){
ll n, k, i, x, w, cnt, left, j;
ld res=0, ans;
cin>>n>>k;
vector<pair<ll, ll>> a(n);
multiset<ll> s;
for(i=0;i<n;++i){
cin>>x>>w;
if(w == -1) w = inf;
a[i] = {w, x};
s.insert(x);
}
sort(a);
for(i=0;i<k;++i){
res += *s.begin();
s.erase(s.begin());
}
for(i=0;i<n;++i){
if(a[i].first == inf or i == k) break;
s.clear();
ans = 0;
cnt = 1;
for(j=0;j<=i;++j){
ans += (ld)a[j].first/(ld)cnt;
++cnt;
}
for(;j<n;++j){
s.insert(a[j].second);
}
for(j=i+1;j<k;++j){
ans += (ld)*s.begin()/(ld)cnt;
s.erase(s.begin());
}
res = min(res, ans);
}
cout<<fixed<<setprecision(20)<<res<<endl;
}
int main() {
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
cout.tie(nullptr);
srand(time(nullptr));
ll t=1;
// cin>>t;
for(;t>0;--t){
solve();
}
return 0;
}
