#include <bits/stdc++.h>
using namespace std;
int main() {
int n, k;
cin >> n >> k;
vector<long long> A(n), B(n);
for (int i = 0; i < n; i++) {
cin >> A[i] >> B[i];
B[i] = (B[i] == -1 ? 1000000000 : B[i]);
}
vector<int> order(n);
iota(order.begin(), order.end(), 0);
sort(order.begin(), order.end(), [&](int i, int j) {
return (B[i] == B[j] ? A[i] > A[j] : B[i] < B[j]);
});
long double ans = 1e9;
for (int m = 0; m <= k; m++) {
vector dp(n + 1, vector<long double>(m + 1, 1e9));
dp[0][0] = 0;
for (int i = 0; i < n; i++) {
for (int j = 0; j <= i && j <= m; j++) {
if (j + 1 <= m) {
dp[i + 1][j + 1] = min(dp[i + 1][j + 1], dp[i][j] + (long double)B[order[i]] / (j + 1));
}
dp[i + 1][j] = min(dp[i + 1][j], dp[i][j] + (long double)A[order[i]] / (m + 1));
}
}
for (int p = m; p <= n; p++) {
vector<long long> C;
for (int i = p; i < n; i++) {
C.push_back(A[order[i]]);
}
sort(C.begin(), C.end());
if ((int)C.size() < k - p) {
break;
}
long double res = dp[p][m];
for (int i = 0; i < k - p; i++) {
res += (long double)C[i] / (m + 1);
}
ans = min(ans, res);
}
}
cout << fixed << setprecision(9) << ans << "\n";
}
