#include <bits/stdc++.h>
using namespace std;
#define int long long
#define INF (int)1e18
#define f first
#define s second
mt19937_64 RNG(chrono::steady_clock::now().time_since_epoch().count());
void Solve()
{
int n, k; cin >> n >> k;
vector <pair<int, int>> a(n);
for (auto &x : a) {
cin >> x.s >> x.f;
if (x.f == -1) x.f = INF;
}
sort(a.begin(), a.end());
double ans = INF;
for (int i = 0; i <= k; i++){
vector <double> dp(k + 1, INF); //how many A's taken
dp[0] = 0;
// cout << "OKING " << i << "\n\n";
for (int j = 0; j < n; j++){
vector <double> ndp(k + 1, INF);
for (int j1 = 0; j1 <= k; j1++){
if (j1 != k)
ndp[j1 + 1] = min(ndp[j1 + 1], dp[j1] + (double)a[j].s / (i + 1));
int pos = j + 1 - j1;
if (pos < 1) continue;
if (pos <= i) ndp[j1] = min(ndp[j1], dp[j1] + (double)a[j].f / pos);
else ndp[j1] = min(ndp[j1], dp[j1]);
}
// cout << "LOL " << j << "\n";
// for (auto &x : ndp) cout << x << " ";
// cout << "\n";
dp = ndp;
}
// cout << "\n";
ans = min(ans, dp[k - i]);
}
cout << fixed << setprecision(10) << ans << "\n";
}
int32_t main()
{
auto begin = std::chrono::high_resolution_clock::now();
ios_base::sync_with_stdio(0);
cin.tie(0);
int t = 1;
// cin >> t;
for(int i = 1; i <= t; i++)
{
//cout << "Case #" << i << ": ";
Solve();
}
auto end = std::chrono::high_resolution_clock::now();
auto elapsed = std::chrono::duration_cast<std::chrono::nanoseconds>(end - begin);
cerr << "Time measured: " << elapsed.count() * 1e-9 << " seconds.\n";
return 0;
}
