#include <bits/stdc++.h>
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define int long long
#define yes() cout << "YES\n"
#define no() cout << "NO\n"
using namespace std;
using ll = long long;
using ull = unsigned long long;
using ld = long double;
const int inf = 1e9;
const int mod = 1e9 + 7;
const int maxn = 1e6 + 10;
const int mod1 = 998244353;
const int mod2 = 1e18 + 1;
const int mod3 = 1e9 + 9;
const int mod4 = 333333333;
const int mod5 = 200000;
const int mod6 = 10007;
const int k = 300;
const int w = 1e5;
const ld EPS = 1e-8;
int LOG = 30;
void solve() {
int n, k1;
cin >> n >> k1;
vector<pair<ld, ld>> a(n);
for (auto& i : a) {
cin >> i.first >> i.second;
if (i.second == -1) i.second = inf;
}
sort(all(a), [](pair<ld, ld> a, pair<ld, ld> b) {
return a.second < b.second || (a.second == b.second && a.first < b.first);
});
ld ans = inf;
vector<vector<vector<ld>>> dp(n, vector<vector<ld>> (n + 1, vector<ld> (n + 1, inf)));
for (int i = 0; i < n; i++) {
dp[i][0][0] = 0;
dp[i][1][1] = a[i].second;
dp[i][0][1] = a[i].first;
}
for (int i = 0; i < n; i++) {
for (int j = 0; j <= n; j++) {
for (int k = 1; k <= n; k++) {
for (int i1 = 0; i1 < i; i1++) {
ld cnt = j;
if (j != 0) dp[i][j][k] = min({dp[i][j][k], dp[i1][j - 1][k - 1] + a[i].second / cnt, dp[i1][j][k - 1] + a[i].first / (cnt + 1)});
else dp[i][j][k] = min(dp[i][j][k], dp[i1][j][k - 1] + a[i].first);
}
}
}
}
for (int i = 0; i < n; i++) {
for (int j = 0; j <= n; j++) {
for (int k = 0; k <= n; k++) {
if (k >= k1) ans = min(ans, dp[i][j][k]);
}
}
}
cout << ans << "\n";
}
signed main() {
cout.precision(16);
ios::sync_with_stdio(false);
cin.tie(nullptr);
int t = 1;
// cin >> t;
while (t--) {
solve();
}
}
