#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef long double ld;
typedef unsigned long long ull;
#define len(v) (int)((v).size())
const int inf = 1e9;
inline void solve(){
ll n, k;
cin >> n >> k;
vector<ll> a(n), b(n);
for (int i = 0; i < n; ++i){
cin >> a[i] >> b[i];
}
vector<int> inds(n);
for (int i = 0; i < n; ++i){
inds[i] = i;
}
sort(inds.begin(), inds.end(), [&](int i, int j){
if (b[i] == -1 && b[j] == -1) return false;
if (b[i] == -1 || b[j] == -1) return b[i] != -1;
return b[i] < b[j];
});
ld ans = 1e100;
for (int i = 0; i <= n; ++i){
if (i > 0 && b[inds[i - 1]] == -1) break;
ld time = 0;
for (int j = 0; j < i; ++j){
time += b[inds[j]] / (ld)(j + 1);
}
vector<ll> rm;
for (int j = i; j < n; ++j){
rm.push_back(a[inds[j]]);
}
sort(rm.begin(), rm.end());
for (int j = 0; j < k - i; ++j){
time += rm[j] / (ld)(i + 1);
}
ans = min(ans, time);
}
cout << ans << '\n';
}
signed main() {
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
cout.tie(nullptr);
cout.precision(60);
int t = 1;
// cin >> t;
while (t--) {
solve();
}
}
