#include<bits/stdc++.h>
#define optimizar_io ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);cout.setf(ios::fixed);cout.precision(15);
#pragma GCC optimize("Ofast")
using namespace std;
typedef long long ll;
#define x first
#define y second
pair<double,double> cad[501];
double sol(ll l,ll n,ll m)
{
vector<vector<vector<double>>> dp(2,vector<vector<double>>(m+3,vector<double>(m+3,1e9)));
dp[0][1][1]=0;
double bs=1e9;
for(int i=1; i<=n; i++)
{
for(int j=1; j<=m+1; j++)
{
for(int k=1; k<=m+1; k++)
{
double temp=1e9;
temp=min(temp,dp[0][j][k]);
temp=min(temp,dp[0][j][k-1]+cad[i].y/l);
if(cad[i].first!=-1&&j!=1)
temp=min(temp,dp[0][j-1][k-1]+cad[i].x/(j-1));
dp[1][j][k]=temp;
if(k==m+1&&j==l) bs=min(bs,dp[1][j][k]);
}
//cout<<"\n";
}
swap(dp[0],dp[1]);
//cout<<"\n\n";
}
return bs;
}
int main()
{
optimizar_io
ll n,m;
cin>>n>>m;
cad[0]={-1,-1};
for(int i=1; i<=n; i++)
cin>>cad[i].second>>cad[i].first;
sort(cad,cad+n+1);
double bs=1e9;
for(int i=1; i<=m+1; i++)
{
bs=min(sol(i,n,m),bs);
//cout<<sol(i,n,m)<<" ";
}
cout<<bs;
}
