#include <bits/stdc++.h>
using namespace std;
#define int long long
#define ll long long
#define ii pair<ll,ll>
#define fi first
#define se second
#define puf push_front
#define pof pop_front
#define pub push_back
#define pob pop_back
#define lb lower_bound
#define ub upper_bound
#define rep(x,s,e) for (auto x=(s)-((s)>(e));x!=(e)-((s)>(e));((s)<(e))?x++:x--)
#define all(x) (x).begin(),(x).end()
#define sz(x) (int) (x).size()
mt19937 rng(chrono::system_clock::now().time_since_epoch().count());
int n,k;
ii arr[505];
int speed;
float memo[505][505];
float dp(int j,int k){ //we consider j A and k B
if (j+k==0) return 0;
if (memo[j][k]!=-1) return memo[j][k];
float res=1e6;
if (j) res=min(res,dp(j-1,k)+(float)arr[j+k].fi/speed);
if (k) res=min(res,dp(j,k-1)+(float)arr[j+k].se/k);
return memo[j][k]=res;
}
int best[505][505];
signed main(){
cin.tie(0);
cout.tie(0);
cin.sync_with_stdio(false);
cin>>n>>k;
rep(x,1,n+1) cin>>arr[x].fi>>arr[x].se;
int num=0;
rep(x,1,n+1){
if (arr[x].se!=-1) num++;
else arr[x].se=1e9;
}
sort(arr+1,arr+n+1,[](ii i,ii j){
return i.se<j.se;
});
vector<int> v;
rep(x,n+1,1){
v.pub(arr[x].fi);
sort(all(v));
int curr=0;
rep(y,0,sz(v)){
curr+=v[y];
best[x][y+1]=curr;
}
}
float ans=1e6;
rep(x,0,min(num,k)+1){
speed=x+1;
rep(x,0,505) rep(y,0,505) memo[x][y]=-1;
rep(y,x,k+1){
ans=min(ans,dp(y-x,x)+(float)best[y+1][k-y]/speed);
}
}
cout<<fixed<<setprecision(12)<<ans<<endl;
}
