#ifdef __AVX2__
#pragma GCC target "avx2"
#endif
#pragma GCC optimize "O3"
#pragma GCC optimize "unroll-loops"
#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
using namespace std;
#define int long long
#define elif else if
#define all(l) begin(l),end(l)
#define rall(l) rbegin(l),rend(l)
#define append push_back
#define print(l) for(auto i:l) cout<<i<<' '; cout<<endl;
#define pprint(a,b) cout<<a<<' '<<b<<endl;
#define inp(l) for(auto &i:l) cin>>i;
#define ordered_set tree<int, null_type,less<int>, rb_tree_tag,tree_order_statistics_node_update>
#define pai make_pair
#define endl "\n"
#define pii pair<int,int>
#define fi first
#define se second
#define vec vector
// const int mod=998244353;
const int mod1=998244353;
const int mod=1e9+7;
const int N=1e2+5;
int dp[N][N][N];
int iter=1,itera=1;
void solve(){
int n,k;
cin>>n>>k;
vec<int>a(n),b(n);
int cn=0;
for(int i=0;i<n;i++){
cin>>a[i]>>b[i];
if(b[i]<0) b[i]=1e15;
}
vec<vec<int>>b1,a1;
for(int i=0;i<n;i++){
if(b[i]>=0)
b1.append({b[i],b[i]-a[i],i});
a1.append({a[i],i});
}
sort(all(a1));
sort(all(b1));
double ans=1e18;
for(int c=0;c<=k;c++){
double x=0;
vec<bool>vis(n,0);
int col=1,tem=0;
// cout<<c<<endl;
for(int i=0;i<c;i++){
x+=(b1[i][0]+.0)/col;
vis[b1[i][2]]=1;
col++;
tem++;
}
// print(vis)
int p=0;
while(tem<k){
if(!vis[a1[p][1]]){
tem++;
x+=(a1[p][0]+.0)/col;
vis[a1[p][1]]=1;
}
p++;
}
// print(vis)
ans=min(ans,x);
}
cout<<ans<<endl;
}
signed main(){
// freopen("","r",stdin);
// freopen("","w",stdout);
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cout.tie(NULL);
cout<<fixed<<setprecision(20);
// cin>>itera;
for(iter=1;iter<=itera;iter++) solve();
}
