// File election.cpp created on 29.09.2025 at 20:44:48
#include <bits/stdc++.h>
using i64 = long long;
#ifdef DEBUG
#include "/home/ahmetalp/Desktop/Workplace/debug.h"
#else
#define debug(...) void(23)
#endif
constexpr int inf = int(1E6);
template<typename T>
bool chmin(T& a, T b) {
if (a > b) {
a = b;
return true;
}
return false;
}
int main() {
std::ios::sync_with_stdio(false);
std::cin.tie(nullptr);
std::cout << std::fixed << std::setprecision(9);
int N, K;
std::cin >> N >> K;
std::vector<std::array<int, 2>> A(N);
for (int i = 0; i < N; ++i) {
std::cin >> A[i][0] >> A[i][1];
if (A[i][1] == -1) {
A[i][1] = inf;
}
}
std::sort(A.begin(), A.end(), [&](auto lhs, auto rhs) {
return std::pair{lhs[1], lhs[0]} < std::pair{rhs[1], rhs[0]};
});
auto solve = [&](int x) -> double {
std::vector<double> f(N + 1, inf), g(N + 1, inf);
f[0] = 0;
for (int k = 0; k < N; ++k) {
std::vector<double> nf(N + 1, inf), ng(N + 1, inf);
for (int j = 0; j <= std::min(k, K); ++j) {
int i = k - j;
if (i == x - 1) {
chmin(ng[i + j + 1], f[j] + 1.d * A[k][1] / (i + 1));
} else {
chmin(nf[j], f[j] + 1.d * A[k][1] / (i + 1));
}
chmin(nf[j + 1], f[j] + 1.d * A[k][0] / (x + 1));
}
for (int i = 0; i <= std::min(k, K); ++i) {
chmin(ng[i], g[i]);
chmin(ng[i + 1], g[i] + 1.d * A[k][0] / (x + 1));
}
f = std::move(nf);
g = std::move(ng);
}
return g[K];
};
double ans = 0;
{
auto B = A;
std::sort(B.begin(), B.end());
for (int i = 0; i < K; ++i) {
ans += B[i][0];
}
debug(ans);
}
for (int i = 1; i <= K; ++i) {
double res = solve(i);
debug(res);
ans = std::min(ans, res);
}
std::cout << ans << '\n';
return 0;
}
