#include <bits/stdc++.h>
using namespace std;
using i64 = long long;
template <typename A, typename B>
string to_string(pair<A, B> p);
template <typename A, typename B, typename C>
string to_string(tuple<A, B, C> p);
template <typename A, typename B, typename C, typename D>
string to_string(tuple<A, B, C, D> p);
string to_string(const string& s) {
return '"' + s + '"';
}
string to_string(const char* s) {
return to_string((string) s);
}
string to_string(bool b) {
return (b ? "true" : "false");
}
string to_string(vector<bool> v) {
bool first = true;
string res = "{";
for (int i = 0; i < static_cast<int>(v.size()); i++) {
if (!first) {
res += ", ";
}
first = false;
res += to_string(v[i]);
}
res += "}";
return res;
}
template <size_t N>
string to_string(bitset<N> v) {
string res = "";
for (size_t i = 0; i < N; i++) {
res += static_cast<char>('0' + v[i]);
}
return res;
}
template <typename A>
string to_string(A v) {
bool first = true;
string res = "{";
for (const auto &x : v) {
if (!first) {
res += ", ";
}
first = false;
res += to_string(x);
}
res += "}";
return res;
}
template <typename A, typename B>
string to_string(pair<A, B> p) {
return "(" + to_string(p.first) + ", " + to_string(p.second) + ")";
}
template <typename A, typename B, typename C>
string to_string(tuple<A, B, C> p) {
return "(" + to_string(get<0>(p)) + ", " + to_string(get<1>(p)) + ", " + to_string(get<2>(p)) + ")";
}
template <typename A, typename B, typename C, typename D>
string to_string(tuple<A, B, C, D> p) {
return "(" + to_string(get<0>(p)) + ", " + to_string(get<1>(p)) + ", " + to_string(get<2>(p)) + ", " + to_string(get<3>(p)) + ")";
}
void debug_out() { cout << endl; }
template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T) {
cout << " " << to_string(H);
debug_out(T...);
}
#ifdef LOCAL
#define debug(...) cout << "[" << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__)
#else
#define debug(...) 42
#endif
int main() {
cin.tie(nullptr)->sync_with_stdio(false);
#ifdef LOCAL
freopen("input.txt", "r", stdin);
freopen("output.txt", "w", stdout);
#endif
auto solve = [&]() {
int n, k;
cin >> n >> k;
vector<int> a(n), b(n);
for (int i = 0; i < n; i++) {
cin >> a[i] >> b[i];
if (b[i] == -1) {
b[i] = 1e9;
}
}
vector<int> ord(n);
iota(ord.begin(), ord.end(), 0);
sort(ord.begin(), ord.end(), [&](auto i, auto j) {
return b[i] < b[j];
});
vector g(n + 1, vector<int>(k + 1, 1e9));
g[n][0] = 0;
for (int i = n - 1; i >= 0; i--) {
g[i] = g[i + 1];
for (int j = 0; j < k; j++) {
g[i][j + 1] = min(g[i][j + 1], g[i + 1][j] + a[ord[i]]);
}
}
double ans = g[0][k];
for (int x = 1; x <= k; x++) {
vector<double> f(x + 1, 1e9);
f[0] = 0;
for (int i = 0; i < k; i++) {
int p = ord[i];
vector<double> nf(x + 1, 1e9);
for (int j = 0; j <= x; j++) {
nf[j] = min(nf[j], f[j] + 1.0 * a[p] / (x + 1));
if (j < x) {
nf[j + 1] = min(nf[j + 1], f[j] + 1.0 * b[p] / (j + 1));
}
}
f = nf;
ans = min(ans, f[x] + 1.0 * g[i + 1][k - i - 1] / (x + 1));
}
}
cout << fixed << setprecision(9) << ans << '\n';
};
solve();
return 0;
}
