#include<iostream>
#include<vector>
#include<algorithm>
#include<math.h>
#include<set>
#include<iomanip>
using namespace std;
#define ll long long
#define pii pair<ll,ll>
#define mp make_pair
#define endl "\n"
#define out(x) cout << #x << " = " << x << endl
#define outp(x) cout << #x << ".first = " << x.first << " " << #x << ".second = " << x.second << endl
#pragma GCC optimize("Ofast")
#define lll __int128
// enumerate the num of collaborators, from 0 to k-1
// it is optimal to collect all collaborators first, then give speeches
// if we know which collaborators to choose, it's better to choose the ones with smaller b first
void chmin(double &a, double x){
if (x<a) a=x;
}
ll n,k;
pii arr[505];
bool subtask1 = true, subtask2 = true;
// 看到第i個人，拿到了j票，目前people = p，最少時間
double dp[105][105][105];
bool comp(pii a, pii b){
if (a.second != b.second) return a.second < b.second;
return a.first < b.first;
}
signed main(){
ios::sync_with_stdio(false); cin.tie(0);
cin>>n>>k;
for (int i=1;i<=n;i++) {
cin>>arr[i].first>>arr[i].second;
if (arr[i].second != -1) subtask1 = false;
if (arr[i].second != -1 && arr[i].second != arr[i].first) subtask2 = false;
if (arr[i].second == -1) arr[i].second = 1e9;
}
if (subtask1){
sort(arr+1,arr+n+1);
int ans = 0;
for (int i=1;i<=k;i++) ans+=arr[i].first;
cout<<ans<<endl;
return 0;
}
sort(arr+1,arr+1+n,comp);
double best = 1e15;
for (ll goalp=1;goalp<=k;goalp++){ // 枚舉要選幾個collab
for (int i=1;i<=n;i++) for (int j=0;j<=100;j++) for (int p=0;p<=100;p++) dp[i][j][p] = 1e15;
dp[1][0][1] = 0; dp[1][1][1] = arr[1].first/goalp; dp[1][1][2] = arr[1].second;
for (ll i=1;i<=n;i++) for (int j=0;j<=i;j++) for (int p=1;p<=min(goalp,i+1);p++){
//cout<<i<<" "<<j<<" "<<p<<" "<<dp[i][j][p]<<endl;
chmin(dp[i+1][j][p], dp[i][j][p]);
chmin(dp[i+1][j+1][p], dp[i][j][p] + 1.0*arr[i+1].first/goalp); // 「只拿到票的」要等拿完所有collab再選
if (arr[i+1].second != 1e9) chmin(dp[i+1][j+1][p+1], dp[i][j][p] + 1.0*arr[i+1].second/p);
}
best = min(best, dp[n][k][goalp]);
}
cout<<fixed<<setprecision(13);
cout<<best<<endl;
}
