#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 ans_vl[maxn];
double get_ans(int n, int k, vector<double> &a, vector<pair<double, int>> &s_b, int cnt_all) {
if (ans_vl[cnt_all] >= 0.5) {
return ans_vl[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 = cnt_nw; 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]);
}
}
}
ans_vl[cnt_all] = ans;
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 = get_ans(n, k, a, s_b, 0);
double vl = 0;
int p_prv = 0;
int l = 0, r = k;
while (l < r - 1) {
int m1, m2;
double ans1, ans2;
if (l == 0 && r == k) {
int aa = l + (r - l) / 2.6;
int bb = l + (r - l) - (aa - l);
ans1 = get_ans(n, k, a, s_b, aa);
ans2 = get_ans(n, k, a, s_b, bb);
m1 = aa, m2 = bb;
} else {
int aa = l + (r - l) / 2.6;
int bb = l + (r - l) - (aa - l);
if (abs(aa - p_prv) < abs(bb - p_prv)) {
aa = p_prv;
ans1 = vl;
ans2 = get_ans(n, k, a, s_b, bb);
} else {
bb = p_prv;
ans2 = vl;
ans1 = get_ans(n, k, a, s_b, aa);
}
m1 = aa, m2 = bb;
}
if (m1 == l || m2 == l || m1 == r || m2 == r) {
break;
}
ans = min(ans, min(ans1, ans2));
if (ans1 >= ans2) {
l = m1;
vl = ans2;
p_prv = m2;
} else {
r = m2;
vl = ans1;
p_prv = m1;
}
}
for (int i = l + 1; i < r; ++i) {
ans = min(ans, get_ans(n, k, a, s_b, i));
}
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;
}
