#include <iostream>
#include <vector>
#include <iomanip>
#include <algorithm>
using namespace std;
const int N = 1005;
long double dp[N][N], a[N], b[N], inf = 1000000, Ans = inf, o = 1, cst;
signed main(){
cout<<fixed<<setprecision(10);
int n, k;
cin>>n>>k;
vector<pair<int, int>> vec = {{0, 0}};
for (int i=1;i<=n;i++){
cin>>a[i]>>b[i];
if (b[i] == -1)
b[i] = 1001;
vec.push_back({b[i], a[i]});
}
sort(begin(vec) + 1, end(vec));
for (int c=1;c<=n and vec[c - 1].first != 1001;c++){
for (int i=0;i<N;i++){
for (int j=0;j<N;j++)
dp[i][j] = inf;
}
dp[0][0] = 0;
for (int i=1;i<=n;i++){
for (int v=0, clb;v<i;v++){
clb = i - v, cst = 0;
if (clb < c){
if (vec[i].first != 1001)
cst = (o * vec[i].first) / (o * clb);
else
cst = inf;
}
dp[i][v] = min(dp[i][v], dp[i-1][v] + cst);
}
for (int v=1;v<=i;v++)
dp[i][v] = min(dp[i][v], dp[i-1][v - 1] + (o * vec[i].second) / (o * c));
}
Ans = min(Ans, dp[n][k - c + 1]);
}
cout<<Ans<<'\n';
}
