#pragma GCC optimize("O3")
#include <bits/stdc++.h>
using namespace std;
constexpr int maxn = 501, inf = 1e9 + 7;
constexpr double eps = 1e-4;
double dp[maxn][maxn][maxn];
double get_ans(int n, int k, vector<double> &a, vector<pair<double, int>> &s_b, int cnt_all) {
for (int i = 0; i <= n; ++i) {
for (int cnt_nw = 0; cnt_nw <= i && cnt_nw <= cnt_all; ++cnt_nw) {
for (int cnt_used = 0; cnt_used <= k; ++cnt_used) {
dp[i][cnt_nw][cnt_used] = inf;
}
}
}
dp[0][0][0] = 0;
double ans = inf;
for (int i = 0; i < n; ++i) {
for (int cnt_nw = 0; cnt_nw <= i && cnt_nw <= cnt_all; ++cnt_nw) {
for (int cnt_used = 0; cnt_used < k; ++cnt_used) {
if (s_b[i].first < 10000 && cnt_nw < cnt_all) {
dp[i + 1][cnt_nw + 1][cnt_used + 1] = min(dp[i + 1][cnt_nw + 1][cnt_used + 1], dp[i][cnt_nw][cnt_used] + s_b[i].first / (cnt_nw + 1));
if (cnt_used + 1 == k && cnt_nw + 1 == cnt_all) {
ans = min(ans, dp[i + 1][cnt_nw + 1][cnt_used + 1]);
}
}
dp[i + 1][cnt_nw][cnt_used + 1] = min(dp[i + 1][cnt_nw][cnt_used + 1], dp[i][cnt_nw][cnt_used] + a[s_b[i].second] / (cnt_all + 1));
if (cnt_used + 1 == k && cnt_nw == cnt_all) {
ans = min(ans, dp[i + 1][cnt_nw][cnt_used + 1]);
}
dp[i + 1][cnt_nw][cnt_used] = min(dp[i + 1][cnt_nw][cnt_used], dp[i][cnt_nw][cnt_used]);
}
}
}
return ans;
}
void solve() {
int n, k;
cin >> n >> k;
vector<double> a(n), b(n);
vector<pair<double, int>> s_b;
for (int i = 0; i < n; ++i) {
cin >> a[i] >> b[i];
if (b[i] > 0) {
s_b.emplace_back(b[i], i);
} else {
s_b.emplace_back(inf, i);
}
}
sort(s_b.begin(), s_b.end());
double ans = inf, ans_prv = inf;
for (int cnt_all = 0; cnt_all < k; ++cnt_all) {
ans = min(ans, get_ans(n, k, a, s_b, cnt_all));
if (abs(ans - ans_prv) < eps) {
break;
}
ans_prv = ans;
}
cout << ans << '\n';
}
signed main() {
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
cout.precision(25);
cout << fixed;
int t = 1;
// cin >> t;
while (t--) {
solve();
}
return 0;
}
