#include<bits/stdc++.h>
#define F first
#define S second
#define MAX 500
#define oo 1e9+7
#define mod 1000000007
#define fast_in ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);cout.setf(ios::fixed);cout.precision(3);
using namespace std;
typedef long long ll;
typedef long double db;
#define pll pair<ll , ll>
#define vll vector<ll>
#define vvll vector<vll>
#define vpll vector<pll>
ll t,n,mn[MAX],m,l[MAX];
pll aux[MAX];
db dp[MAX][MAX],cost[MAX];
pair<db,db> a[MAX];
int main(){
fast_in
cin>>n>>m;t=n;
for(int i=0;i<n;i++){
cin>>a[i].S>>a[i].F;
if(a[i].F==-1){a[i].F=oo;t--;}
aux[i]={a[i].S,a[i].F};
mn[i]=a[i].S;
}
sort(a,a+n);sort(mn,mn+n);sort(aux,aux+n);
ll s=0,top=m-1;
for(int i=0;i<n;i++){
aux[i]={aux[i].S,i};
if(i<m)s+=mn[i];
l[i]=i;
}sort(aux,aux+n);
for(int i=0;i<m;i++){
cost[i]=s;
if(aux[i].S<top){
s-=mn[aux[i].S];
if(aux[i].S>0)l[aux[i].S]=l[aux[i].S-1];
}
else{
s-=mn[top];top=l[top-1];
}
}
db r=cost[0];
cost[m]=s;
for(int k=0;k<=min(t,m);k++){
for(int j=0;j<=k;j++){
for(int i=0;i+k<=m;i++){
dp[i][j]=oo;
if(i+j==0)dp[i][j]=0;
if(i>0)dp[i][j]=min(dp[i][j],dp[i-1][j]+a[i+j-1].S/(k+1));
if(j>0)dp[i][j]=min(dp[i][j],dp[i][j-1]+a[i+j-1].F/j);
// if(i>0)cout<<dp[i-1][j][k]<<"+"<<a[i+j-1].S/k<<".\n";
// if(j>0)cout<<dp[i][j-1][k]<<"+"<<a[i+j-1].F/j<<"'\n";
if(j==k){
// cout<<i<<" "<<k<<" "<<" "<<dp[i][k][k]<<"+"<<cost[i+k]<<"\n";
if(cost[i+k]==0)r=min(r,dp[i][j]);
else r=min(r,dp[i][j]+cost[i+k]/(k+1));
}
}
}
}
cout<<r;
return 0;
}
