#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define sz(x) (int)size(x)
#define all(x) (x).begin(), (x).end()
constexpr double inf = 1e18;
double pmin(double &a, double b){
return a = min(a, b);
}
int main(){
cin.tie(0)->sync_with_stdio(false);
int n, k;
cin >> n >> k;
vector<double> a(n), b(n);
for(int i = 0; i < n; i++){
cin >> a[i] >> b[i];
if(b[i] < 0) b[i] = inf;
}
{
vector<int> ord(n);
for(int i = 0; i < n; i++) ord[i] = i;
sort(all(ord), [&](int i, int j){return b[i] < b[j];});
vector<double> a2(n), b2(n);
for(int i = 0; i < n; i++) a2[i] = a[ord[i]], b2[i] = b[ord[i]];
a = a2, b = b2;
}
vector<int> ordA(n);
for(int i = 0; i < n; i++) ordA[i] = i;
sort(all(ordA), [&](int i, int j){return a[i] < a[j];});
double ans = inf;
for(int l = 0; l <= k; l++){
vector<vector<double>> dp(k+1, vector<double>(l+1, inf));
dp[0][0] = 0;
for(int i = 0; i < k; i++){
for(int j = 0; j <= l; j++){
if(j < l) pmin(dp[i+1][j+1], dp[i][j] + b[i] / (1+j));
pmin(dp[i+1][j], dp[i][j] + a[i] / (1+l));
}
}
for(int i = l; i <= k; i++){
double val = dp[i][l];
int cnt = i;
for(int j : ordA){
if(j >= i && cnt < k){
val += a[j] / (1+l);
cnt++;
}
}
ans = min(ans, val);
}
}
cout << setprecision(6) << fixed << ans << "\n";
}
