#include<bits/stdc++.h>
using namespace std;
#define IOS cin.tie(nullptr)->sync_with_stdio(0),cin.exceptions(cin.failbit);
#define lb(x) (x)&-(x)
#define all(x) (x).begin(),(x).end()
#define ll long long
constexpr int maxN=5e2+5;
int n,k;
double dp[2][maxN];
pair<double,double> val[maxN];
inline double DP(int G){
fill(dp[0],dp[0]+k+1,1e18);
fill(dp[1],dp[1]+k+1,1e18);
dp[0][0] = 0;
for(int i = 1;i<=n;i++)for(int j = 0;j<=k;j++){
dp[i&1][j] = dp[i&1^1][j];
if(j)dp[i&1][j] = min(dp[i&1][j],dp[i&1^1][j-1]+(j<=G?val[i].first/j:val[i].second/(G+1)));
}
return dp[n&1][k];
}
int main(){
IOS
cin>>n>>k;
for(int i = 1;i<=n;i++){
cin>>val[i].second>>val[i].first;
if(val[i].first==-1)val[i].first = 1e10;
}
sort(val+1,val+n+1);
double ans = 1e18;
for(int i = 0;i<=k;i++)ans = min(ans,DP(i));
cout<<fixed<<setprecision(15)<<ans<<'\n';
}
