#include<bits/stdc++.h>
using namespace std;
#define int long long
#pragma GCC optimize("O3,unroll-loops")
#define fir first
#define sec second
#define pb push_back
signed main(){
ios_base::sync_with_stdio(0);
cin.tie(0);cout.tie(0);
int n,k;
cin>>n>>k;
int a[n+1],b[n+1];
vector<pair<int,int> >bgs;
priority_queue<int>pakai;
priority_queue<int,vector<int>,greater<int> > tmp;
for(int q=1;q<=n;q++){
cin>>a[q]>>b[q];
if(b[q]!=-1)bgs.pb({b[q],a[q]});
else tmp.push(a[q]);
}
sort(bgs.begin(),bgs.end());
int ans[n+2]; memset(ans,0,sizeof ans);
int sum=0;
if(k>=bgs.size()){
for(int q=1;q<=max(0LL,k-(int)bgs.size());q++){
int apa=tmp.top(); tmp.pop();
pakai.push(apa); sum+=apa;
}
ans[bgs.size()]=sum;
}
for(int q=(int)bgs.size()-1;q>=k;q--){
pair<int,int>cur=bgs[q];
tmp.push(cur.sec);
}
for(int q=min(k-1,(int)bgs.size()-1);q>=0;q--){
pair<int,int>cur=bgs[q];
tmp.push(cur.sec);
ans[q]=ans[q+1];
while(pakai.size()<k-q){
int apa=tmp.top(); tmp.pop();
pakai.push(apa);
ans[q]+=apa;
}
while(tmp.size() && pakai.size() && tmp.top()<pakai.top()){
int bu=tmp.top(),ms=pakai.top();
tmp.pop(),pakai.pop();
tmp.push(ms),pakai.push(bu);
ans[q]+=(bu-ms);
}
//cout<<ans[q]<<"K"<<q<<endl;
}
double tot=0;
double mn=ans[0];
for(int q=1;q<=min(k,(int)bgs.size());q++){
tot+=(double)(bgs[q-1].first)/(double)(q);
double brp=(double)(ans[q])/(double)(q+1);
mn=min(mn,tot+brp);
}
cout<<fixed<<setprecision(10)<<mn<<endl;
}
