#include <bits/stdc++.h>
using namespace std;
#define int long long
const int MAX = 5e2 + 5;
void minimize(double &a, const double &b) {
a = min(a, b);
}
int sum[MAX][MAX];
double f[2][MAX];
pair<int, int> state[MAX];
int32_t main() {
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
// freopen("test.inp", "r", stdin); freopen("test.out", "w", stdout);
int n, k;
cin >> n >> k;
int g = 0;
for (int i = 1; i <= n; i++) {
cin >> state[i].first >> state[i].second;
if (state[i].second == -1) state[i].second = 1e9;
else ++g;
}
sort(state + 1, state + n + 1, [](const pair<int, int> &a, const pair<int, int> &b) -> bool {
if (a.second != b.second) return a.second < b.second;
return a.first < b.first;
});
memset(sum, 0x3f, sizeof sum);
for (int i = 1; i <= n; i++) {
sum[i][0] = 0;
for (int j = i; j <= n; j++) {
for (int z = k; z > 0; z--) {
sum[i][z] = min(sum[i][z], sum[i][z - 1] + state[j].first);
}
}
}
sum[n + 1][0] = 0;
double ans = sum[1][k];
g = min(g, k);
for (int c = 0; c <= g; c++) {
for (int i = 0; i < 2; i++) {
for (int j = 0; j <= k; j++) {
f[i & 1][j] = 1e9;
}
}
f[0][0] = 0.0;
for (int i = 1; i <= k; i++) {
for (int j = 0; j <= i; j++) {
f[i & 1][j] = f[(i - 1) & 1][j] + 1.0 * state[i].first / (c + 1);
if (j) minimize(f[i & 1][j], f[(i - 1) & 1][j - 1] + 1.0 * state[i].second / j);
if (j == c) {
minimize(ans, f[i & 1][j] + 1.0 * sum[i + 1][k - i] / (c + 1));
}
}
}
}
cout << fixed << ans;
return 0;
}
