#include <bits/stdc++.h>
using namespace std;
const int nx=505;
int n, m;
vector<pair<int, int>> v(nx);
double dp[nx][nx], sm[nx][nx], ans;
int32_t main()
{
cin.tie(NULL)->sync_with_stdio(false);
cin>>n>>m;
v.resize(n);
for (int i=0; i<n; i++)
{
cin>>v[i].second>>v[i].first;
if (v[i].first==-1) v[i].first=1e9;
}
sort(v.begin(), v.end());
for (int i=1; i<=m; i++) sm[n+1][i]=1e9;
for (int i=n;i>=1; i--) for (int j=1; j<=m; j++) sm[i][j]=min(sm[i+1][j], sm[i+1][j-1]+v[i-1].second); //cout<<"sm "<<i<<' '<<j<<' '<<sm[i][j]<<'\n';
ans=sm[1][m];
for (int i=1; i<=m; i++)
{
for (int j=0; j<=m; j++) for (int k=0; k<=i; k++) dp[j][k]=1e9;
dp[0][1]=0;
for (int j=1; j<=m; j++)
{
for (int k=1; k<=i; k++)
{
dp[j][k]=dp[j-1][k]+(double)v[j-1].second/i;
if (k>1&&v[j-1].first<=1000) dp[j][k]=min(dp[j][k], dp[j-1][k-1]+((double)v[j-1].first)/(k-1));
//cout<<"debug "<<i<<' '<<j<<' '<<k<<' '<<dp[j][k]<<'\n';
}
ans=min(ans, dp[j][i]+sm[j+1][m-j]/i);
//cout<<i<<' '<<j<<' '<<dp[j][i]+sm[j+1][m-j]/i<<'\n';
}
}
cout<<fixed<<setprecision(12)<<ans;
}
