#include <bits/stdc++.h>
using namespace std;
#define int long long
#define ld long double
vector <pair <ld, ld>> arr = {};
// vector <pair <ld, ld>> arr = {};
vector <ld> minvs(502);
vector <int> cntin(1002);
// int sum = 0;
vector <vector <ld>> dp(502, vector <ld> (502, -1));
ld dps(int cur, int ck, int k, int cuk, int n) {
if(cuk == ck) {
ld a = ck+1;
return minvs[cur]/a;
}
if(cur == k) {
return 1e18;
}
if(dp[cur][cuk] != -1) {
return dp[cur][cuk];
}
// int totalm = 1e18;
ld a = cuk+1;
ld data = dps(cur+1, ck, k, cuk+1, n)+(arr[cur].second/a);
a = ck+1;
ld data2 = dps(cur+1, ck, k, cuk, n)+(arr[cur].first/a);
return dp[cur][cuk] = min(data, data2);
}
signed main() {
//your code goes here
int n;
cin >> n;
int k;
cin >> k;
for(int i = 0; i < n; i++) {
ld a, b;
cin >> a >> b;
if(b == -1) {
b = 1e18;
}
arr.push_back({a, b});
// arr2.push_back({a, b});
}
sort(arr.begin(), arr.end(), [&](auto& left, auto& right) {
return left.second < right.second;
});
// sort(arr2.begin(), arr2.end(), [&](auto& left, auto& right) {
// return left.first < right.first;
// });
// for(int i = 0; i < k; i++) {
// sum += arr2[i].first;
// cntin[arr2[i].first] = i+1;
// }
// for(int i = 0; i < n; i++) {
// cout << arr[i].first << " " << arr[i].second << endl;
// }
ld sum = 0;
vector <ld> ar = {};
for(int i = k; i < n; i++) {
ar.push_back(arr[i].first);
}
sort(ar.begin(), ar.end());
int ch = 0;
for(int i = k; i >= 0; i--) {
// cout << "HELLO" << endl;
sum = 0;
if(ar.size() == 0) {
if(i == 0) {
break;
}
ld v2 = arr[i-1].first;
ar.push_back(v2);
continue;
}
// auto it = ar.begin();
// ld v = *it;
// sum += v;
// ar.erase(it);
for(int j = 0; j < ((k-i)); j++) {
sum += ar[j];
}
minvs[i] = sum;
if(i == 0) {
break;
}
ld v2 = arr[i-1].first;
ar.push_back(v2);
sort(ar.begin(), ar.end());
}
// for(int i = 0; i <= k; i++) {
// cout << minvs[i] << " ";
// }
// cout << endl;
ld totalm = 1e18;
for(int i = 0; i <= k; i++) {
for(int i = 0; i <= n; i++) {
for(int j = 0; j <= k; j++) {
dp[i][j] = -1;
}
}
ld data = dps(0, i, k, 0, n);
totalm = min(totalm, data);
// if(i == 0) {
// cout << data << " " << totalm << endl;
// }
// cout << data << endl;
}
cout << totalm << endl;
return 0;
}
