#include <bits/stdc++.h>
using namespace std;
typedef long double ld;
const ld inf = 1e16;
int n, k;
const int MAXN = 525;
pair <int, int> a[MAXN];
ld pre[MAXN][MAXN];
int main () {
cin >> n >> k;
for (int i = 1; i <= n; i++) cin >> a[i].first >> a[i].second;
cout << fixed << setprecision(9);
sort(a + 1, a + n + 1, [&] (pair <int, int> &x, pair <int, int> &y) {
if (x.second == -1) return bool(0);
return x.second == y.second ? x.first < y.first : ((y.second == -1) || (x.second < y.second));
});
for (int i = 0; i < MAXN; i++) for (int j = 0; j < MAXN; j++) pre[i][j] = inf;
for (int i = 1; i <= n; i++) {
vector <int> xx;
for (int j = i; j <= n; j++) xx.push_back(a[j].first);
sort(xx.begin(), xx.end());
int sum = 0;
for (int j = 0; j < (int)xx.size(); j++) {
sum += xx[j];
pre[i][j + 1] = sum;
}
pre[i][0] = 0;
}
ld mn = 1e18;
for (int sze = 0; sze <= k; sze++) {
ld dp[n + 1][sze + 1];
for (int j = 1; j <= sze; j++) {
dp[0][j] = inf;
}
dp[0][0] = 0;
mn = min(mn, 1.0 * pre[1][k] / (sze + 1) + dp[0][sze]);
for (int i = 1; i <= n; i++) {
for (int j = 0; j <= sze; j++) dp[i][j] = inf;
for (int j = 0; j <= min(sze, i); j++) {
if (i - j) dp[i][j] = dp[i - 1][j] + 1.0 * a[i].first / (sze + 1);
if (a[i].second != -1 && j) dp[i][j] = min(dp[i][j], dp[i - 1][j - 1] + 1.0 * a[i].second / j);
}
if (k >= i) {
mn = min(mn, 1.0 * pre[i + 1][k - i] / (sze + 1) + dp[i][sze]);
}
if (k == i) {
mn = min(mn, dp[i][sze]);
}
}
}
cout << mn << '\n';
}
