#include <bits/stdc++.h>
using namespace std;
#define int long long
#define dd double
#define minim(X, Y) (X = min(X, Y))
const int Z = 502, INF = 1e18;
int N, K, A[Z], B[Z];
dd ans = INF;
array<int, 2> s[Z];
dd dp[2][Z];
int suf[Z][Z];
int32_t main() {
ios::sync_with_stdio(0), cin.tie(0);
cin >> N >> K;
for(int i = 0; i < N; ++i) {
cin >> A[i] >> B[i];
if(B[i] < 0) B[i] = INF;
s[i] = {B[i], A[i]};
}
sort(s, s + N);
for(int i = 0; i < N; ++i) {
A[i] = s[i][1];
B[i] = s[i][0];
}
for(int i = 0; i < N; ++i) {
vector<int> v;
for(int j = i; j < N; ++j) v.push_back(A[j]);
sort(begin(v), end(v));
for(int j = 0, sum = 0; j < (int)size(v); ++j)
suf[i][j+1] = (sum += v[j]);
}
for(int c = 0; c <= N; ++c) {
fill(dp[1], dp[1] + N + 1, INF);
dp[1][0] = 0;
for(int i = 0; i < N; ++i) {
auto &curr = dp[i & 1];
auto &prev = dp[!(i & 1)];
for(int k = 0; k <= N; ++k)
curr[k] = prev[k] + dd(A[i]) / dd(c + 1);
for(int k = 0; k < N; ++k)
minim(curr[k+1], prev[k] + dd(B[i]) / dd(k + 1));
for(int k = 0; k <= N; ++k) {
int other = (i + 1) - k;
if(other > K - c) curr[k] = INF;
}
int other = K - (i + 1);
if(0 <= other && other <= (N - i - 1))
minim(ans, curr[c] + dd(suf[i+1][other]) / dd(c + 1));
}
}
ans = min(ans, dd(suf[0][K]));
cout << setprecision(10) << fixed << ans;
}
