#include <bits/stdc++.h>
using namespace std;
inline void solve()
{
int n,k;
cin>>n>>k;
vector<pair<int,int>>vals;
for (int i=0;i<n;i++)
{
int a,b;
cin>>a>>b;
b=(b==-1?1e6:b);
vals.push_back({b,a});
}
sort(begin(vals),end(vals));
int ans=1e9+10;
for (int i=0;i<k;i++)
{
int co=0;
if (i>0&&vals[i-1].first==1e6)
break;
for (int j=0;j<i;j++)
co+=round((vals[j].first*1000)/(float)(j+1));
vector<int>vls;
for (int j=i;j<n;j++)
vls.push_back(vals[j].second);
sort(begin(vls),end(vls));
int sm=0;
for (int j=0;j<k-i;j++)
sm+=vls[j];
co+=round((sm*1000)/(float)(i+1));
ans=min(ans,co);
}
cout<<to_string(ans/(float)1000)<<endl;
}
int main()
{
ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL);
int t=1;
// cin>>t;
for (int i=1;i<=t;i++)
{
solve();
}
}
