#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define pll pair<ll, ll>
#define pii pair<int, int>
#define fs first
#define sc second
#define pb push_back
void solve() {
int n,k;
cin>>n>>k;
pii a[n+1];
for(int i=1;i<=n;i++){
cin>>a[i].fs>>a[i].sc;
if(a[i].sc==-1)a[i].sc=1e9;
}
sort(a+1,a+n+1,[&](pii p1,pii p2){return make_pair(p1.sc,p1.fs)<make_pair(p2.sc,p2.fs);});
double ans=1e18;
for(int c=0;c<=k;c++){
double dp[n+1][c+1];
dp[0][0]=0;
for(int i=1;i<=c;i++)dp[0][i]=1e18;
for(int i=1;i<=n;i++){
for(int j=0;j<=c;j++){
dp[i][j]=dp[i-1][j]+1.0*a[i].fs/(1+c);
if(j){
dp[i][j]=min(dp[i][j],dp[i-1][j-1]+1.0*a[i].sc/j);
}
}
}
multiset<int> ss;
for(int i=k+1;i<=n;i++)ss.insert(a[i].fs);
double s=0;
for(int i=k;i>=c;i--){
if(i<k){
ss.insert(a[i+1].fs);
int x=*ss.begin();
s+=1.0*x/(1+c);
ss.erase(ss.find(x));
}
ans=min(ans,dp[i][c]+s);
}
ans=min(ans,dp[k][c]);
}
cout<<fixed<<setprecision(5)<<ans<<'\n';
}
int main() {
ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
solve();
}
