#include <algorithm>
#include <iostream>
using namespace std;
const int N = 500;
const int INF = 0x3f3f3f3f;
int aa[N], bb[N], ii[N];
int aa_[N], ss[N];
double dp[N + 1];
int main() {
ios_base::sync_with_stdio(false), cin.tie(NULL);
int n, m; cin >> n >> m;
for (int i = 0; i < n; i++) {
cin >> aa[i] >> bb[i], ii[i] = i;
if (bb[i] == -1)
bb[i] = INF;
}
sort(ii, ii + n, [] (int i, int j) { return bb[i] < bb[j]; });
for (int h = 0; h < m; h++) {
int n_ = 0;
for (int h_ = h; h_ < n; h_++)
aa_[n_++] = aa[ii[h_]];
sort(aa_, aa_ + n_);
int s = 0;
for (int z = 0; z < m - h; z++)
s += aa_[z];
ss[h] = s;
}
double ans = ss[0];
for (int k_ = 1; k_ <= m; k_++) {
for (int k = 0; k <= k_; k++)
dp[k] = INF;
dp[0] = 0;
for (int h = 0; h < m; h++) {
int i = ii[h], a = aa[i], b = bb[i];
for (int k = k_; k >= 0; k--) {
double x = dp[k] + (double) a / (k_ + 1);
if (k && b != INF)
x = min(x, dp[k - 1] + (double) b / k);
dp[k] = x;
}
if (h + 1 < m)
ans = min(ans, dp[k_] + (double) ss[h + 1] / (k_ + 1));
}
}
printf("%.14f\n", ans);
return 0;
}
