#include<bits/stdc++.h>
using namespace std;
using ll=long long;
using ld=long double;
//#pragma GCC optimize("03,unroll-loops")
//#pragma GCC target("avx2")
//#pragma GCC target("sse4")
#define all(v) v.begin(),v.end()
#define F first
#define S second
#define pub push_back
#define pob pop_back
#define puf push_front
#define pof pop_front
//#define randi uniform_int_distribution<long long>
#define damoon(v) v.resize(unique(all(v))-v.begin())
//mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
//randi dist(0,10000000000000000);
typedef pair<int,int> pii;
typedef pair<long long,long long> pll;
typedef pair<int,bool> pib;
typedef pair<long long,bool> plb;
typedef pair<int,pii> pip;
typedef pair<pii,int> ppi;
typedef vector<int> veci;
typedef vector<long long> vecl;
typedef vector<bool> vecb;
typedef vector<pll> vecp;
typedef set<int> seti;
typedef set<long long> setl;
typedef set<pii> setp;
typedef map<int,int> mapii;
typedef map<long long,long long> mapll;
typedef map<int,bool> mapib;
typedef map<long long,bool> maplb;
const int mod=1e9+7,neginf=-1e9,N=500;
const ll inf=2e18;
const double PI=acos(-1);
ll a[N+5],b[N+5],sum[N+5];
ld dp[2][N+5][N+5];
void solve()
{
ll n,k;
cin>>n>>k;
vecp v(1);
for(int i=1;i<=n;i++)
{
cin>>a[i]>>b[i];
if(b[i]==-1)
b[i]=inf;
v.pub(pll(b[i],a[i]));
}
sort(all(v));
for(int i=0;i<2;i++)
for(int j=0;j<=n;j++)
for(int l=0;l<=n;l++)
dp[i][j][l]=inf;
vecl krj;
for(int i=n;i>=1;i--)
{
krj.pub(v[i].S);
sort(all(krj));
if(k-i+1<=(int)krj.size())
{
for(int kk=0;kk<k-i+1;kk++)
sum[i]+=krj[kk];
}
else
{
sum[i]=inf;
}
}
ld ans=inf;
ans=min(ans,(ld)sum[1]);
for(int i=0;i<=k;i++)
dp[0][0][i]=0;
for(int i=1;i<=k;i++)
{
for(int kk=0;kk<=i;kk++)
{
for(int l=0;l<=k;l++)
{
dp[i&1][kk][l]=inf;
if(kk and v[i].F!=inf)
dp[i&1][kk][l]=min(dp[i&1][kk][l],dp[(i&1)^1][kk-1][l]+(1/(1.0*kk))*(1.0*v[i].F));
dp[i&1][kk][l]=min(dp[i&1][kk][l],dp[(i&1)^1][kk][l]+(1/(1.0*(l+1)))*(1.0*v[i].S));
}
}
for(int j=0;j<=i;j++)
ans=min(ans,sum[i+1]*(1/(1.0*(j+1)))+dp[i&1][j][j]);
}
cout<<fixed<<setprecision(15)<<ans<<"\n";
}
int main()
{
cin.tie(0);
cout.tie(0);
ios_base::sync_with_stdio(false);
//ifstream fin("in.txt");
//ofstream fout("out.txt");
int t=1;
//cin>>t;
while(t--)
{
solve();
}
}
