#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef double db;
#define all(x) (x).begin(), (x).end()
#define md ((tl + tr) >> 1)
#define TL v + v, tl, md
#define TR v + v + 1, md + 1, tr
#define F first
#define S second
#define pii pair<int, int>
#define int ll
const int maxn = 5e5 + 7;
const ll inf = 1e9 + 7;
const double PI = atan2(0.0, -1.0);
int n, k, a[505], b[505], mn[505][505];
db dp[505][505];
vector<int> v[505];
pii p[505];
void solve() {
cin >> n >> k;
for (int i = 1; i <= n; i++) {
cin >> a[i] >> b[i];
if (b[i] == -1)
b[i] = inf;
}
for (int i = 1; i <= n; i++)
p[i] = {b[i], a[i]};
sort(p + 1, p + n + 1);
for (int i = n; i >= 1; i--) {
v[i] = v[i + 1];
v[i].push_back(p[i].S);
sort(all(v[i]));
for (int j = 0; j < v[i].size(); j++)
mn[i][j + 1] = mn[i][j] + v[i][j];
}
for (int i = 1; i <= k; i++) {
dp[i][0] = dp[i - 1][0] + p[i].S;
for (int j = 1; j < i; j++)
dp[i][j] = min(dp[i - 1][j - 1] + p[i].F / (db)j, dp[i - 1][j] + p[i].S / (db)(j + 1));
dp[i][i] = dp[i - 1][i - 1] + p[i].F / (db)i;
}
db res = inf;
for (int i = 0; i <= k; i++) {
for (int j = 0; j <= i; j++) {
if (k - j <= n - i)
res = min(res, dp[i][j] + mn[i + 1][k - j] / (db)(j + 1));
}
}
cout << fixed << setprecision(10) << res;
}
signed main() {
ios_base::sync_with_stdio(false);
cin.tie(0);
int test = 1;
// cin >> test;
while (test--) {
solve();
// cout << '\n';
}
return 0;
}
