#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace std;
using namespace __gnu_pbds;
template<typename T> using Tree = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
typedef long long int ll;
typedef long double ld;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;
#define fastio ios_base::sync_with_stdio(false); cin.tie(NULL)
#define pb push_back
#define endl '\n'
#define sz(a) (int)a.size()
#define setbits(x) __builtin_popcountll(x)
#define ff first
#define ss second
#define conts continue
#define ceil2(x,y) ((x+y-1)/(y))
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
#define yes cout << "Yes" << endl
#define no cout << "No" << endl
#define rep(i,n) for(int i = 0; i < n; ++i)
#define rep1(i,n) for(int i = 1; i <= n; ++i)
#define rev(i,s,e) for(int i = s; i >= e; --i)
#define trav(i,a) for(auto &i : a)
template<typename T>
void amin(T &a, T b) {
a = min(a,b);
}
template<typename T>
void amax(T &a, T b) {
a = max(a,b);
}
#ifdef LOCAL
#include "debug.h"
#else
#define debug(x) 42
#endif
/*
*/
const int MOD = 1e9 + 7;
const int N = 1e5 + 5;
const int inf1 = int(1e9) + 5;
const ll inf2 = ll(1e18) + 5;
void solve(int test_case)
{
ll n,k; cin >> n >> k;
vector<pll> a(n);
rep(i,n) cin >> a[i].ff >> a[i].ss;
rep(i,n) if(a[i].ss == -1) a[i].ss = inf2;
auto cmp = [&](pll p1, pll p2){
return p1.ss < p2.ss;
};
sort(all(a),cmp);
ld ans = inf2;
rep(mask,1<<n){
ld cost = 0;
ll guys = 1;
ll votes = 0;
vector<ll> others;
bool ok = true;
rep(i,n){
if(mask&(1<<i)){
if(a[i].ss == inf2){
ok = false;
}
else{
cost += a[i].ss/(ld)guys;
guys++;
votes++;
}
}
else{
others.pb(a[i].ff);
}
}
if(!ok) conts;
sort(rall(others));
while(votes < k){
ll x = others.back();
others.pop_back();
cost += (ld)x/guys;
votes++;
}
amin(ans,cost);
}
cout << fixed << setprecision(11);
cout << ans << endl;
}
int main()
{
fastio;
int t = 1;
// cin >> t;
rep1(i, t) {
solve(i);
}
return 0;
}
