#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
int main() {
ios::sync_with_stdio(0);
cin.tie(0);
int n, k;
cin >> n >> k;
vector<array<int, 2>> a(n);
for (int i = 0; i < n; ++i) {
for (int j = 0; j < 2; ++j) {
cin >> a[i][j];
}
swap(a[i][0], a[i][1]);
}
//~ for (int i = 0; i < n; ++i) {
//~ cout << a[i][0] << " " << a[i][1] << "\n";
//~ }
//~ cerr << "\n";
ld res = 1e9 + 1;
for (int add = 0; add < 2; ++add) {
for (int i = 0; i <= n; ++i) {
ld mult = 1, tim = 0;
//~ vector<vector<double>>
bool bad = false;
vector<array<int, 2>> na = a;
for (int j = 0; j < i; ++j) {
if (j + add < i) {
sort(rbegin(na), rend(na), [&](array<int, 2> x, array<int, 2> y) {
if (x[0] == -1) return false;
if (y[0] == -1) return true;
return x[0] < y[0];
});
} else {
sort(rbegin(na), rend(na), [&](array<int, 2> x, array<int, 2> y) {
if (x[0] == -1) return false;
if (y[0] == -1) return true;
return x[0] * (mult + 1) + y[1] * mult < y[0] * (mult + 1) + x[1] * mult;
});
}
auto now = na.back();
na.pop_back();
if (now[0] == -1) {
bad = true;
break;
}
//~ cerr << now[1] << " " << now[0] << "\n";
tim += 1.0 * now[0] / mult;
mult += 1;
}
//~ cerr << "Done picked!\n";
if (bad) {
//~ cerr << "bad!\n";
continue;
}
if (mult - 1 >= k) {
//~ cout << i << " = " << tim << "\n";
res = min(res, tim);
continue;
}
vector<vector<ld>> dp(n + 1, vector<ld>(k + 1, 1e9 + 1));
dp[i][mult - 1] = tim;
reverse(begin(na), end(na));
for (int j = i; j < n; ++j) {
//~ cerr << na[j - i][1] << " " << na[j - i][0] << "\n";
for (int t = 0; t <= k; ++t) {
dp[j + 1][t] = min(dp[j + 1][t], dp[j][t]);
if (t + 1 <= k) {
//~ cerr << dp[j][t] << " + " << 1.0 * na[j - i][1] / mult << "\n";
dp[j + 1][t + 1] = min(dp[j + 1][t + 1],
dp[j][t] + 1.0 * na[j - i][1] / mult);
}
}
}
//~ cout << i << " = " << dp[n][k] << "\n";
res = min(res, dp[n][k]);
}
}
cout << fixed << setprecision(3) << res << "\n";
}
