#include <bits/stdc++.h>
using namespace std;
#ifdef LOCAL
#include "debug.h"
#else
#define debug(...) 0
#endif
const int N = 500;
const double INF = 1e18;
int main() {
ios::sync_with_stdio(false);
cin.tie(NULL);
int n, k;
cin >> n >> k;
static array<int, 2> p[N];
for (int i = 0; i < n; i++) {
int a, b;
cin >> a >> b;
if (b == -1) b = 1e9;
p[i] = {b, a};
}
sort(p, p + n);
static int g[N][N + 1];
for (int i = 0; i < n; i++) {
static int t[N];
for (int j = i; j < n; j++) t[j - i] = p[j][1];
sort(t, t + n - i);
g[i][0] = 0;
for (int j = 1; j <= n - i; j++) g[i][j] = g[i][j - 1] + t[j - 1];
}
double ans = g[0][k];
for (int t = 0; t <= k; t++) {
static double f[N + 1];
for (int i = 0; i <= t; i++) f[i] = INF;
f[0] = 0;
for (int i = 0; i < n; i++) {
for (int j = t; j >= 0; j--)
f[j] = min(f[j] + (double)p[i][1] / (t + 1),
j == 0 ? INF : f[j - 1] + (double)p[i][0] / j);
if (k - i - 1 >= 0)
ans = min(ans, f[t] + (double)g[i + 1][k - i - 1] / (t + 1));
}
}
cout << fixed << setprecision(12) << ans << '\n';
return 0;
}
