#include <cstdio>
#include <stdio.h>
#include <stdbool.h>
#include <iostream>
#include <map>
#include <vector>
#include <climits>
#include <stack>
#include <string>
#include <queue>
#include <algorithm>
#include <set>
#include <unordered_set>
#include <unordered_map>
#include <cmath>
#include <cctype>
#include <bitset>
#include <iomanip>
#include <cstring>
#include <numeric>
#include <cassert>
#include <random>
#include <chrono>
#include <fstream>
using namespace std;
#define int long double
#define pii pair<int, int>
#define mp make_pair
#define pb push_back
#define fi first
#define se second
bool custom(pii a, pii b){
return a.se<b.se;
}
int32_t main(){
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
int n, k, ans=LLONG_MAX/2;
cin>>n>>k;
vector<pii> vect(n);
for (int i=0; i<n; ++i){
cin>>vect[i].fi>>vect[i].se;
if (vect[i].se==-1)vect[i].se=INT_MAX/2;
}
sort(vect.begin(), vect.end(), custom);
for (int i=0; i<=k; ++i){
vector<int> dp(k-i+1, LLONG_MAX/2);
dp[0]=0;
for (int j=0; j<n; ++j)for (int l=k-i; l>=0; --l){
if (0<j-l+1&&j-l+1<=i)dp[l]+=vect[j].se/(j-l+1);
if(l)dp[l]=min(dp[l], dp[l-1]+vect[j].fi/(i+1));
}
ans=min(ans, dp[k-i]);
}
cout<<fixed<<setprecision(9)<<ans;
}
