#include<bits/stdc++.h>
using namespace std;
#define int long long
#define double long double
#pragma GCC optimize("O3,unroll-loops")
#define fir first
#define sec second
#define pb push_back
int n,k;
vector<pair<int,int> >tmp;
double brp(int m){
vector<vector<double> >dp(n+1,vector<double>(k+1,1e18));
dp[0][0]=0;
for(int q=1;q<=n;q++){
for(int w=0;w<=min(k,q);w++){
// ambil a nya
if(w)dp[q][w]=min(dp[q][w],dp[q-1][w-1]+(double)(tmp[q].second)/(double)(m+1));
// ambil b nya
if((q-w)>m){
dp[q][w]=min(dp[q][w],dp[q-1][w]);
}
else{
dp[q][w]=min(dp[q][w],dp[q-1][w]+(double)(tmp[q].first)/(double)(q-w));
}
//cout<<q<<" "<<w<<" "<<dp[q][w]<<endl;
}
}
return dp[n][k-m];
}
signed main(){
ios_base::sync_with_stdio(0);
cin.tie(0);cout.tie(0);
cin>>n>>k;
int a[n+1],b[n+1];
tmp.push_back({0,0});
int hah=0;
for(int q=1;q<=n;q++){
cin>>a[q]>>b[q];
if(b[q]==-1)tmp.push_back({1e18,a[q]});
else tmp.push_back({b[q],a[q]}),hah++;
}
sort(tmp.begin(),tmp.end());
int l=0,r=min(k,hah);
// for(int q=0;q<=k;q++){
// cout<<brp(q)<<endl;
// }
double ans=1e18;
while(r-l>2){
int mid1=l+(r-l)/3;
int mid2=r-(r-l)/3;
double satu=brp(mid1),dua=brp(mid2);
if(satu<dua){
ans=min(ans,satu);
r=mid2-1;
}
else{
ans=min(ans,dua);
l=mid1+1;
}
}
for(int q=l;q<=r;q++){
ans=min(ans,brp(q));
}
cout<<fixed<<setprecision(10)<<ans<<endl;
}
