#include <bits/stdc++.h>
using namespace std;
#define rep(i, a, b) for(int i = a; i < (b); ++i)
#define all(x) begin(x), end(x)
#define sz(x) (int)(x).size()
#define F first
#define S second
#define pb push_back
typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;
int main() {
cin.tie(0)->sync_with_stdio(0);
cin.exceptions(cin.failbit);
int n;cin>>n;
int k;cin>>k;
vector<pair<pair<ll,ll>,int>> bya(n);
rep(i,0,n)cin>>bya[i].F.F>>bya[i].F.S;
sort(all(bya));
rep(i,0,n)bya[i].S=i;
vector<pair<pair<ll,ll>,int>> byb = bya;
sort(all(byb), [&](auto a, auto b){
if(a.F.S == -1) return false;
if(b.F.S == -1) return true;
return a.F.S < b.F.S;
});
while(sz(byb) && byb.back().F.S == -1) byb.pop_back();
// for(auto p : bya) cout<< p.F.F<<' '<<p.F.S<<' '<<p.S<<endl;
// cout<<endl;
// for(auto p : byb) cout<< p.F.F<<' '<<p.F.S<<' '<<p.S<<endl;
double fast = 1e18;
rep(u,0,min(k,sz(byb))+1){
double time = 0;
set<int> have;
rep(i,0,u){
time += (double)byb[i].F.S/(1+i);
have.insert(byb[i].S);
}
int need = k-u;
rep(i,0,n){
if(need==0) break;
if(have.count(i)) continue;
time += (double)bya[i].F.F/(u+1);
need--;
}
fast = min(fast, time);
}
cout<<fixed<<setprecision(10)<<fast<<endl;
}
