#include <bits/stdc++.h>
using namespace std;
#define int long long
const int N = 505;
const int inf = 1ll << 60;
int n,k,a[N],b[N];
long double eval(int x){
if((k-x) < 0){
return inf;
}
long double dp[n+2][n+2];
for(int i = 0;i<=n;i++){
for(int j = 0;j<=n;j++){
dp[i][j] = 1e18 + 7;
}
}
dp[0][0] = 0;
for(int i = 0;i<n;i++){
for(int j = 0;j<=n;j++){
//ai alır
dp[i+1][j+1] = min(dp[i+1][j+1] , dp[i][j] + (long double)a[i] / (long double)(x+1));
//bi / almaz
if((i+1-j) <= x){
dp[i+1][j] = min(dp[i+1][j] , dp[i][j] + (long double)b[i] / (long double)(i+1-j));
}
else {
dp[i+1][j] = min(dp[i+1][j] , dp[i][j]);
}
}
}
return dp[n][k-x];
}
void solve(){
cin >> n >> k;
pair < int , int > arr[n];
int sayac = n;
for(int i = 0;i<n;i++){
cin >> arr[i].second >> arr[i].first;
if(arr[i].first == -1){
arr[i].first = inf;
sayac--;
}
}
sort(arr , arr + n);
for(int i = 0;i<n;i++){
a[i] = arr[i].second;
b[i] = arr[i].first;
}
long double ans = 1e18 + 7;
for(int i = 0;i<=sayac;i++){
ans = min(ans , eval(i));
}
cout << fixed << setprecision(9) << ans << endl;
}
signed main(){
ios_base::sync_with_stdio(0);cin.tie(0);
int testcase = 1;//cin >> testcase;
while(testcase--)solve();
}
/*
obs1 : almadıklarımdan ilk x tanesini kesin alcam
dp[i][j] -> şimdiye kadar kaç tane aldım
*/
