#include<bits/stdc++.h>
using ll = long long;
signed main() {
std::cin.tie(nullptr)->sync_with_stdio(false);
int n, k;
std::cin >> n >> k;
std::vector<std::pair<int, int>> data(n);
for (auto& [x, y] : data) std::cin >> x >> y;
double ans = 1e18;
for (int i = 0; i <= k - 1; ++i) {
auto a = data;
std::sort(a.begin(), a.end(), [&](auto x, auto y) {
if (x.second == -1) return false;
if (y.second == -1) return true;
return x.second < y.second;
});
double cur = 0;
for (int j = 0; j < i; ++j) {
if (a[j].second == -1) cur = 1e18;
else cur += 1.0 * a[j].second / (j + 1);
}
a.erase(a.begin(), a.begin() + i);
std::sort(a.begin(), a.end(), [&](auto x, auto y) {
return x.first < y.first;
});
for (int j = 0; j < k - i; ++j) {
cur += 1.0 * a[j].first / (i + 1);
}
ans = std::min(ans, cur);
}
std::cout << std::fixed << std::setprecision(15) << ans;
}
