#include <bits/stdc++.h>
using namespace std;
int main() {
ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
int N, K; cin >> N >> K;
vector< pair<int, int> > states(N);
for (int i = 0; i < N; ++i) {
cin >> states[i].second >> states[i].first;
if (states[i].first == -1)
states[i].first = 1'000'000'000;
}
sort(begin(states), end(states));
double ans = 1e18;
for (int g = 0; g <= K; ++g) {
vector< vector<double> > dp(N + 1, vector<double>(K - g + 1, 1e18));
dp[0][0] = 0;
for (int i = 0; i < N; ++i)
for (int j = 0; j <= K - g; ++j) {
if (j < K - g)
dp[i + 1][j + 1] = min(dp[i + 1][j + 1], dp[i][j] + (double) states[i].second / (g + 1));
dp[i + 1][j] = min(dp[i + 1][j], dp[i][j] + (i - j < g ? (double) states[i].first / (i - j + 1) : .0));
}
ans = min(ans, dp[N][K - g]);
}
cout << setprecision(9) << fixed << ans << '\n';
return 0;
}
