#include<bits/stdc++.h>
#define fi first
#define se second
using namespace std;
const int INF=1e6+7;
const int N=500;
pair<int,int> t[N+10];
double dp[N+10][N+10];
double solve(int n,int k,int m)
{
for(int j=1;j<=m;j++)
dp[0][j]=INF;
for(int i=1;i<=k;i++)
{
dp[i][0]=dp[i-1][0]+(double)t[i].fi/(m+1);
//cerr<<dp[i][0]<<" ";
for(int j=1;j<=m;j++)
{
dp[i][j]=min(dp[i-1][j]+(double)t[i].fi/(m+1),dp[i-1][j-1]+(double)t[i].se/j);
if(j>i)
dp[i][j]=INF;
//cerr<<dp[i][j]<<" \n"[j==m];
}
}
priority_queue<int> pq;
for(int i=n;i>k;i--)
pq.push(-t[i].fi);
int w=0;
double ans=INF;
for(int i=k;i>=m;i--)
{
ans=min(ans,dp[i][m]+(double)w/(m+1));
pq.push(-t[i].fi);
w-=pq.top();
pq.pop();
}
return ans;
}
int main()
{
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cout.tie(NULL);
int n,k;
cin>>n>>k;
for(int i=1;i<=n;i++)
{
cin>>t[i].fi>>t[i].se;
if(t[i].se==-1)
t[i].se=INF;
}
sort(t+1,t+n+1,[](pair<int,int> a,pair<int,int> b){ return a.se<b.se; });
double ans=INF;
//cerr<<solve(n,k,3)<<"\n";
//return 0;
for(int m=0;m<=k;m++)
{
//cerr<<"m="<<m<<": "<<solve(n,k,m)<<"\n";
ans=min(ans,solve(n,k,m));
}
cout<<fixed<<setprecision(4)<<ans<<"\n";
return 0;
}
