#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.f >> x.s;
swap(x.f, x.s);
if (x.f == -1) x.f = INF;
}
sort(a.begin(), a.end());
vector<vector<double>> dp(k + 1, vector<double>(k + 1, INF));
dp[0][0] = 0;
for (auto x : a){
// cout << x.f << " " << x.s << "\n";
vector<vector<double>> ndp(k + 1, vector<double>(k + 1, INF));
for (int i = 0; i <= k; i++){
for (int j = 0; j <= i; j++){
ndp[i][j] = min(ndp[i][j], dp[i][j]);
if (i != k){
ndp[i + 1][j] = min(ndp[i + 1][j], dp[i][j] + (double)x.s / (j + 1));
if (x.f < 1001)
ndp[i + 1][j + 1] = min(ndp[i + 1][j + 1], dp[i][j] + (double)x.f / (j + 1));
}
}
}
dp = ndp;
// for (int i = 0; i <= k; i++){
// for (int j = 0; j <= k; j++){
// cout << dp[i][j] << " ";
// }
// cout << "\n";
// }
// cout << "\n";
}
double mn = INF;
for (int i = 0; i <= k; i++) mn = min(mn, dp[k][i]);
cout << fixed << setprecision(10) << mn << "\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;
}
