#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef long double ld;
const ll N = 5e2;
const ll inf = 1e18;
struct state{
ll a,b;
}v[N];
int p[N];
ld dp[N + 1][N + 1];
ll sum[N + 1];
vector<int> v2;
int main(){
cout<<fixed<<setprecision(5);
int n,k;
ld ans = inf;
cin>>n>>k;
for(int i = 0;i < n;i++){
cin>>v[i].a>>v[i].b;
if(v[i].b == -1)v[i].b = inf;
p[i] = i;
}
sort(p,p + n,[&](int a, int b){
return v[a].b < v[b].b;
});
for(int i = n;i >= 0;i--){
///first i - 1 complete
v2.clear();
for(int j = i;j < n;j++){
v2.push_back(v[p[j]].a);
}
sort(v2.begin(),v2.end());
for(int j = 0;j < k - i;j++){
sum[i]+=v2[j];
}
}
for(int m = 0;m < k;m++){
for(int i = 0;i <= n;i++){
for(int j = 0;j <= n;j++){
dp[i][j] = inf;
}
}
dp[0][0] = 0;///i as j bs
for(int i = 0;i <= n;i++){
int id = p[i];
for(int j = 0;j <= i;j++){
if(i - j + 1 <= n)dp[i - j + 1][j] = min(dp[i - j + 1][j],dp[i - j][j] + (ld)v[id].a/(m + 1));
if(j + 1 <= n)dp[i - j][j + 1] = min(dp[i - j][j + 1],dp[i - j][j] + (ld)v[id].b/(j + 1));
}
}
for(int i = 0;i + m <= n;i++){
ans = min(ans,dp[i][m] + (ld)sum[i + m]/(m + 1));
}
}
cout<<ans;
return 0;
}
/**
7 5
284 758 x 474
288 668 380
320 635 315
333 702 x 369
374 676 302
375 666 x 291
393 646 x 253
**/
