#include<bits/stdc++.h>
using namespace std;
#define int long long
#define double long double
bool cmp(pair<int,int>a,pair<int,int>b){
if(a.second==-1 && b.second==-1){
return a.first<b.first;
}
else if(a.second==-1)return false;
else if(b.second==-1)return true;
if(a.second!=b.second)return a.second<b.second;
return a.first<b.first;
}
signed main(){
int n,k;
cin>>n>>k;
pair<int,int>isi[n+1];
for(int q=1;q<=n;q++){
cin>>isi[q].first>>isi[q].second;
}
sort(isi+1,isi+n+1,cmp);
int suff[n+2][k+1];
for(int q=1;q<=k;q++){
suff[n+1][q]=1e18;
}
suff[n+1][0]=0;
for(int q=n;q>=1;q--){
for(int w=0;w<=k;w++){
suff[q][w]=1e18;
// ambil
if(w!=0){
suff[q][w]=min(suff[q][w],suff[q+1][w-1]+isi[q].first);
}
// ga
suff[q][w]=min(suff[q][w],suff[q+1][w]);
// cout<<suff[q][w]<<" ";
}
// cout<<endl;
}
double ans=1e18;
double dp[k+1][k+1];
for(int buff=0;buff<=k;buff++){
dp[0][0]=0;
if(buff==0){
double sisa=suff[1][k]/(double)(buff+1);
ans=min(ans,sisa);
}
for(int q=1;q<=k;q++){
dp[0][q]=1e18;
}
for(int q=1;q<=k;q++){
for(int w=0;w<=buff;w++){
dp[q][w]=1e18;
if(q<w)continue;
// ambil buff
if(w!=0 && isi[q].second!=-1){
double waktu=(double)isi[q].second/(double)(w);
dp[q][w]=min(dp[q][w],dp[q-1][w-1]+waktu);
}
// ga ambil b
double waktu=(double)isi[q].first/(double)(buff+1);
dp[q][w]=min(dp[q][w],dp[q-1][w]+waktu);
if(w==buff){
double sisa=suff[q+1][k-q]/(double)(buff+1);
ans=min(ans,dp[q][w]+sisa);
}
}
}
}
cout<<fixed<<setprecision(10)<<ans<<endl;
}
