#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#define ordered_set tree<int, null_type,less<int>, rb_tree_tag,tree_order_statistics_node_update>
using namespace __gnu_pbds;
using namespace std;
#define pb push_back
#define st first
#define nd second
typedef long long ll;
typedef long double ld;
const ll I = 1000'000'000'000'000'000LL;
const int II = 2'000'000'000;
const ll M = 1000'000'007LL;
const int N = 1000'007;
pair<int, int> tab[N];
pair<int, int> t2[N];
void Solve()
{
int n, k;
ld ans = II, cur = 0;
cin >> n >> k;
for(int i = 1; i <= n; ++i)
{
cin >> tab[i].nd >> tab[i].st;
if(tab[i].st == -1) tab[i].st = II;
}
sort(tab + 1, tab + 1 + n);
for(int i = 1; i <= n; ++i)
t2[i] = make_pair(tab[i].nd, i);
sort(t2 + 1, t2 + 1 + n);
for(int i = 0; i < k; ++i)
{
if(tab[i].st == II) break;
if(i > 0) cur += (ld)((ld)tab[i].st / (ld)i);
int il = k - i;
ld sum = 0;
for(int j = 1; j <= n && il > 0; ++j)
{
if(t2[j].nd <= i) continue;
--il;
sum += (ld)((ld)t2[j].st / (ld)(i + 1));
}
ans = min(ans, sum + cur);
}
cout << fixed << setprecision(9) << ans << '\n';
}
int main()
{
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
//int t; cin >> t;
//while(t--)
Solve();
return 0;
}
