#include<bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace std;
using namespace __gnu_pbds;
typedef long long ll;
typedef long double ld;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef vector<int> vect;
#define ordered_set tree<int, null_type, less<int>, rb_tree_tag, tree_order_statistics_node_update>
#define ordered_multiset tree<int, null_type, less_equal<int>, rb_tree_tag, tree_order_statistics_node_update>
#define pb push_back
#define f first
#define s second
bool cmp(const pii& a, const pii& b){
if(a.f == -2) return true;
if(b.f == -2) return false;
if(a.s == -1) return false;
if(b.s == -1) return true;
return a.s < b.s;
}
int main(){
ios_base::sync_with_stdio(0);
cin.tie(0);
int n, k;
cin >> n >> k;
vector<pii> tab(n + 1);
for(int i = 0; i < n; i++){
cin >> tab[i].f >> tab[i].s;
}
tab[n] = {-2, 1e9};
sort(tab.begin(), tab.end(), cmp);
ld wyn = 1e18;
for(int i = 1; i <= k; i++){
vector<ld> dp(n + 1, 1e18);
dp[0] = 0;
for(int j = 1; j <= n; j++){
for(int x = j - 1; x >= 0; x--){
dp[x + 1] = min(dp[x + 1], dp[x] + ld(tab[j].f) / ld(i));
int t = j - x;
if(t < i){
if(tab[j].s != -1){
dp[x] += ld(tab[j].s) / ld(t);
}else{
dp[x] = 1e18;
}
}
}
}
wyn = min(wyn, dp[k - i + 1]);
}
cout << fixed << setprecision(10) << wyn << "\n";
return 0;
}
