#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
using pii = pair<int, int>;
#define pb push_back
#define ff first
#define ss second
const ld inf = 1e9;
int main(){
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
int n, k; cin>>n>>k;
vector<pii> all(n + 1);
for (int i = 1; i <= n; i++){
cin>>all[i].ss>>all[i].ff;
if (all[i].ff == -1) all[i].ff = inf;
}
sort(all.begin() + 1, all.end());
vector<int> a(n + 1), b(n + 1);
for (int i = 1; i <= n; i++){
a[i] = all[i].ss;
b[i] = all[i].ff;
}
vector<vector<int>> f(n + 2, vector<int>(k + 1, inf));
multiset<int> st;
for (int i = n + 1; i > 0; i--){
if (i <= n) st.insert(a[i]);
f[i][0] = 0;
auto it = st.begin();
for (int j = 1; j <= min((int) st.size(), k); j++){
f[i][j] = f[i][j - 1] + (*it);
it++;
}
}
vector<vector<ld>> dp(k + 1, vector<ld>(k + 1));
ld out = inf;
for (int x = 0; x <= k; x++){
for (int i = 1; i <= k; i++){
for (int j = 0; j <= i; j++){
dp[i][j] = inf;
if (j) dp[i][j] = min(dp[i][j], dp[i - 1][j - 1] + 1.0 * a[i] / (x + 1));
if (b[i] != -1 && j < i) dp[i][j] = min(dp[i][j], dp[i - 1][j] + 1.0 * b[i] / (i - j));
}
}
for (int i = x; i <= k; i++){
out = min(out, dp[i][i - x] + 1.0 * f[i + 1][k - i] / (x + 1));
}
}
cout<<fixed<<setprecision(10)<<out<<"\n";
}
