#include <bits/stdc++.h>
#define pb push_back
#define fst first
#define snd second
#define fore(i,a,b) for(int i=a,pao=b;i<pao;++i)
#define SZ(x) ((int)x.size())
#define ALL(x) x.begin(),x.end()
#define mset(a,v) memset((a),(v),sizeof(a))
#define FIN ios::sync_with_stdio(0);cin.tie(0);cout.tie(0)
using namespace std;
typedef long long ll;
const int MAXN=505,INF=1e9;
int A[MAXN],B[MAXN];
int main(){FIN;
int n,k;cin>>n>>k;
vector<pair<int,int>>b;
vector<int>a;
fore(i,0,n){
cin>>A[i]>>B[i];
if(B[i]!=-1)b.pb({B[i],i});
else a.pb(A[i]);
}
double ans=INF;
sort(ALL(b));
fore(i,0,SZ(b)+1){
double tot=0,d=1;
int cnt=0;
fore(j,0,i){
tot+=(double)b[j].fst/d;
d++;
cnt++;
}
vector<int>c;
fore(j,i,SZ(b)){
c.pb(A[b[j].snd]);
}
fore(i,0,SZ(a)){
c.pb(a[i]);
}
sort(ALL(c));
fore(j,0,k-cnt){
tot+=(double)c[j]/d;
}
ans=min(ans,tot);
}
cout<<fixed<<setprecision(20)<<ans<<endl;
}
