#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 = 503;
pair<int, int> tab[N], t2[N];
int czy[N];
set<pair<int, int>> lft;
void Solve()
{
cout << fixed << setprecision(7);
int n, k;
ld ans = II;
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;
for(int j = 1; j <= n; ++j) czy[j] = 0;
lft.clear();
vector<int> cur;
ld s1 = 0, s2 = 0;
for(int j = 1; j <= i; ++j)
{
s1 += (ld)tab[j].st / (ld)j;
cur.pb(j);
}
for(int j = 1; j <= n && (int)lft.size() < k - i; ++j)
{
if(t2[j].nd <= i) continue;
czy[t2[j].nd] = 1;
s2 += (ld)t2[j].st / (ld)(i + 1);
lft.insert(t2[j]);
}
if(i == 0)
{ans = s1 + s2; continue;}
ans = min(ans, s1 + s2);
ld s = s1 + s2;
//cout << "A: " << i << " " << s << "\n";
for(int j = i + 1; j <= n; ++j)
{
if(tab[j].st == II) break;
ld akt = (ld)tab[j].st / (ld)i, bst = I;
if(czy[j])
akt -= (ld)tab[j].nd / (ld)(i + 1);
else
akt -= (ld)(*lft.rbegin()).st / (ld)(i + 1);
int wh = 0;
for(int l = i - 1; l >= 0; --l)
{
ld a = akt - (ld)tab[cur[l]].st / (ld)(l + 1);
a += (ld)tab[cur[l]].nd / (ld)(i + 1);
if(a < bst)
{
bst = a;
wh = l;
}
if(l > 0)
akt += ((ld)tab[cur[l]].st / (ld)l) - ((ld)tab[cur[l]].st / (ld)(l + 1));
}
//cout << j << " " << czy[j] << " " << tab[j].nd << " : " << bst << " " << wh << "\n";
if(bst > 0) continue;
s += bst;
if(czy[j])
lft.erase(make_pair(tab[j].nd, j));
else
lft.erase((*lft.rbegin()));
lft.insert(make_pair(tab[cur[wh]].nd, cur[wh]));
swap(cur[wh], cur.back()); cur.pop_back();
sort(cur.begin(), cur.end()); cur.pb(j);
ans = min(ans, s);
}
}
cout << fixed << setprecision(7) << ans << "\n";
}
int main()
{
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
//int t; cin >> t;
//while(t--)
Solve();
return 0;
}
