#include<bits/stdc++.h>
typedef long double ld;
#define fastio cin.tie(0), cout.tie(0), ios::sync_with_stdio(0);
using namespace std;
#define pii pair<int, int>
#define F first
#define S second
int main(){
fastio
const int big = 5e5+1;
int n, k, T = 0;
cin >> n >> k;
vector<pii> ba(n);
for(int i=0; i<n; i++){
cin >> ba[i].S >> ba[i].F;
if(ba[i].F==-1){
ba[i].F = big;
T++;
}
}
sort(ba.begin(), ba.end());
//s[i] = min sum of k-i elements from [i, n)
T = min(k-1, n-T);
priority_queue<int, vector<int>, greater<int>> pq;
vector<int> s(T+1);
for(int i=T; i<n; i++) pq.push(ba[i].S);
s[T] = 0;
for(int i=0; i<k-T; i++){
s[T] += pq.top();
pq.pop();
}
for(int i=T-1; i>-1; i--){
pq.push(ba[i].S);
s[i] = s[i+1]+pq.top();
pq.pop();
}
//dp by #collaborator
ld ans = big;
for(int t=0; t<=T; t++){
vector<ld> dp(t+1, big);
dp[0] = 0;
for(int i=0; i<k; i++){
if(dp[t]!=big)
ans = min(ans, dp[t]+((ld)s[t])/(t+1));
for(int j=t-1; j>-1; j--){
if(dp[j]==big) continue;
dp[j+1] = min(dp[j+1], dp[j]+((ld)ba[i].F)/(j+1));
dp[j] += ((ld)ba[i].S)/(t+1);
}
}
}
cout << fixed << setprecision(6) << ans << '\n';
return 0;
}
