#include <bits/stdc++.h>
#include <fstream>
using namespace std;
template<class A, class B>
ostream& operator<<(ostream& o, const pair<A, B>& p) {return o << '(' << p.first << ", " << p.second << ')';}
template<size_t Index = 0, typename... Types>
ostream& printTupleElements(ostream& o, const tuple<Types...>& t) {if constexpr (Index < sizeof...(Types)){if(Index > 0){o << ", ";}o << get<Index>(t);printTupleElements<Index + 1>(o, t);}return o;}
template<typename... Types>
ostream& operator<<(ostream& o, const tuple<Types...>& t){o << "(";printTupleElements(o, t);return o << ")";}
template<class T>
auto operator<<(ostream& o, const T& x) -> decltype(x.end(), o){o << '{';bool first = true;for (const auto& e : x){if (!first){o << ", ";}o << e;first = false;} return o << '}';}
#define DEBUG
#ifdef DEBUG
#define fastio()
#define debug(x...) cerr << "[" #x "]: ", [](auto... $) {((cerr << $ << "; "), ...); }(x), cerr << '\n'
#define check(x) if (!(x)) { cerr << "Check failed: " << #x << " in line " << __LINE__ << endl; exit(1); }
#else
#define fastio() ios_base::sync_with_stdio(0); cin.tie(0);
#define debug(...)
#define check(x)
#endif
typedef long long ll;
typedef long double ld;
#define pi pair<int, int>
#define pl pair<ll, ll>
#define st first
#define nd second
#define vi vector<int>
#define vll vector<ll>
#define eb emplace_back
#define all(x) (x).begin(), (x).end()
#define sz(x) (int)(x).size()
void solve() {
//ifstream cin("nazwa.in");
//ofstream cout("nazwa.out");
int n, k;
cin >> n >> k;
vector<pi>sorb;
vector<pi>sora;
int ileb = n;
for(int i = 1; i <= n; i++) {
int a, b;
cin >> a >> b;
if(b == -1) {
ileb--;
b = 1e9;
}
sorb.eb(b, i);
sora.eb(a, i);
}
sort(all(sorb));
sort(all(sora));
ld ans = 1e9;
for(int i = 0; i <= min(k, ileb); i++) {
vector<bool> czy(n + 1, 0);
ld tmpans = 0;
for(int j = 0; j < i; j++) {
tmpans += (ld)sorb[j].st / (ld)(j + 1);
czy[sorb[j].nd] = 1;
}
int ile = k - i;
for(int j = 0; j < n; j++) {
if(!ile) {
break;
}
if(!czy[sora[j].nd]) {
ile--;
tmpans += (ld)sora[j].st / (i + 1);
}
}
ans = min(ans, tmpans);
}
cout.precision(9);
cout << fixed << ans << '\n';
}
int main() {
fastio();
int t;
//cin >> t;
t = 1;
while(t--) {
solve();
}
}
