#include<bits/stdc++.h>
using namespace std;
#define lb long double
const int maxn=510;
const int inf=1e9+7;
bool cmp(pair<int,int> x, pair<int,int> y){
if(x.second!=y.second){
if(x.second==-1) return false;
if(y.second==-1) return true;
return x.second<y.second;
}
return x.first>y.first;
}
int a[maxn], b[maxn], dp1[maxn][maxn];
lb dp2[maxn][maxn];
int main(){
ios_base::sync_with_stdio(false); cin.tie(nullptr); cout.tie(nullptr);
int n, k; cin >> n >> k;
vector<pair<int,int>>process(n);
for(pair<int,int> &p : process) cin >> p.first >> p.second;
sort(process.begin(),process.end(),cmp);
for(int i=1;i<=n;i++){
a[i]=process[i-1].first;
b[i]=process[i-1].second;
}
memset(dp1,1,sizeof(dp1));
dp1[n+1][0]=0;
for(int i=n;i>=1;i--){
for(int j=0;j<=n;j++){
dp1[i][j]=dp1[i+1][j];
if(j) dp1[i][j]=min(dp1[i][j],dp1[i+1][j-1]+a[i]);
}
}
lb resp=dp1[1][k];
for(int x=1;x<=k;x++){ //pegar x caras para serem colaboradores
if(b[x]==-1) break;
for(int i=0;i<=n;i++)
for(int j=0;j<=x;j++) dp2[i][j]=inf;
//cout << x << ":\n";
dp2[0][0]=0;
for(int i=1;i<=n;i++){
for(int j=0;j<=x;j++){
dp2[i][j]=dp2[i-1][j];
lb c1=(lb)a[i]/(lb)(x+1), c2=inf;
if(j&&b[i]!=-1) c2=(lb)b[i]/(lb)j;
//cout << c1 << " " << c2 << endl;
dp2[i][j]=min(dp2[i-1][j]+c1,dp2[i-1][j-1]+c2);
}
lb aux=0;
if(i<=k) aux=dp1[i+1][k-i];
aux/=(lb)(x+1);
resp=min(resp,dp2[i][x]+aux);
//cout << i << ' ' << dp2[i][x] << " " << aux << endl;
}
}
cout << fixed << setprecision(16) << resp << endl;
}
