#include <bits/stdc++.h>
using namespace std;
#define print(l) for(auto i:l) cout<<i<<" ";cout<<endl;
#define input(t,l,n) vector<t>l(n);for(int i = 0;i<n;i++)cin>>l[i];
#define int long long
#define pb push_back
#define ordered_set tree<int, null_type,less<int>, rb_tree_tag,tree_order_statistics_node_update>
#define all(l) l.begin(),l.end()
#define pii pair<int,int>
#define fi first
#define se second
const int M = 1e9+7;
const int inf = 1e18;
int bp(int x, int y, int p){
int res = 1;
x = x % p;
while (y > 0) {
if (y & 1)
res = (res * x) % p;
y = y >> 1;
x = (x * x) % p;
}
return res;
}
int MI(int n, int p){
return bp(n, p - 2, p);
}
int mul(int x,int y, int p){
return x * 1ull * y % p;
}
int di(int x,int y, int p){
return mul(x, MI(y, p), p);
}
int n , m , kk , q;
void solve(int testcase_number){
cin>>n>>kk;
int A[n],B[n];
vector<vector<int>>ord;
vector<int>c;
vector<vector<int>>ck;
for(int i = 0;i<n;i++){
cin>>A[i]>>B[i];
if(B[i] == -1){
c.pb(A[i]);
}
else{
ck.pb({A[i],B[i]});
}
}
sort(all(c));
sort(all(ck));
long double mtime = inf;
for(int i = 0;i<=min(kk,(int)ck.size());i++){
int j = kk-i;
if(j>(int)c.size()) continue;
long double time = 0;
long double mem = 1;
// int mem =1 ;
vector<int>rem = c;
for(int k = 0;k<i;k++){
time+=ck[k][1]/mem;
mem++;
}
for(int k = i;k<ck.size();k++){
rem.pb(ck[k][0]);
}
sort(all(rem));
for(int k = 0;k<j;k++){
time+=rem[k]/mem;
}
// cout<<i<<" "<<j<<" "<<time<<endl;
mtime = min(mtime,time);
}
while(next_permutation(all(ck))){
for(int i = 0;i<=min(kk,(int)ck.size());i++){
int j = kk-i;
if(j>(int)c.size()) continue;
long double time = 0;
long double mem = 1;
// int mem =1 ;
vector<int>rem = c;
for(int k = 0;k<i;k++){
time+=ck[k][1]/mem;
mem++;
}
for(int k = i;k<ck.size();k++){
rem.pb(ck[k][0]);
}
sort(all(rem));
for(int k = 0;k<j;k++){
time+=rem[k]/mem;
}
// cout<<i<<" "<<j<<" "<<time<<endl;
mtime = min(mtime,time);
}
}
cout<<mtime<<endl;
}
signed main(){
ios::sync_with_stdio(0);//DO NOT USE IN INTERACTIVE
cin.tie(0), cout.tie(0);
cout << fixed<<setprecision(9);
int t = 1;
// cin>>t;
for(int i = 1;i<=t;i++){
solve(i);
}
}
