#include <algorithm>
#include <iomanip>
#include <iostream>
#include <utility>
#include <vector>
using namespace std;
#define int long long
using pii = pair<int, int>;
const long double INF = 1e18;
const int maxn = 505;
int n, k;
vector<pii> vc;
long double dp[maxn][maxn];
long double sf[maxn][maxn]; // sf[i][j] 從 A[i~(n-1)] 選 j 個最大的數字
bool cmp(pii a, pii b) {
if (a.second == -1 && b.second == -1) {
return a.first < b.first;
}
if (a.second == -1 || b.second == -1) {
return a.second > b.second;
}
return a.second < b.second;
}
void build_sf() {
for (int i = 0; i < maxn; i++) {
fill(sf[i] + 1, sf[i] + maxn, INF);
}
for (int i = n - 1; i >= 0; i--) {
vector<int> cur;
for (int j = i; j < n; j++) {
cur.push_back(vc[j].first);
}
sort(cur.begin(), cur.end());
for (int j = 1; j <= k; j++) {
if (j > (int)(cur.size()))
break;
else
sf[i][j] = sf[i][j - 1] + cur[j - 1];
}
}
}
long double solve(const int t) {
for (int i = 0; i < n; i++) {
fill(dp[i], dp[i] + (t + 1), INF);
}
for (int i = 0; i < n; i++) {
if (vc[i].second == -1) break;
if (i == 0) {
dp[i][0] = vc[i].first / (t + 1.0);
dp[i][1] = vc[i].second;
continue;
}
for (int j = 0; j <= t; j++) {
if (j == 0) {
dp[i][0] = dp[i - 1][0] + vc[i].first / (t + 1.0);
} else {
long double x = dp[i - 1][j] + vc[i].first / (t + 1.0);
long double y = dp[i - 1][j - 1] + vc[i].second * 1.0 / j;
dp[i][j] = min(x, y);
}
}
}
long double res = sf[0][k];
for (int i = 0; i < n; i++) {
res = min(res, dp[i][t] + sf[i + 1][k - t] / (t + 1.0));
}
return res;
}
signed main() {
ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
cout << fixed << setprecision(15);
cin >> n >> k;
for (int i = 0; i < n; i++) {
int x, y;
cin >> x >> y;
vc.push_back({x, y});
}
sort(vc.begin(), vc.end(), cmp);
build_sf();
long double res = sf[0][k];
for (int t = (1); t < (k + 1); t++) {
res = min(res, solve(t));
}
cout << res << '\n';
return 0;
}
