#define _CRT_SECURE_NO_WARNINGS
#include <bits/stdc++.h>
//#include "temp.cpp"
#include <cstdio>
using namespace std;
#ifndef ONLINE_JUDGE
#define dbg(x) cerr << #x <<" "; print(x); cerr << endl;
#else
#define dbg(x)
#endif
#define sz(x) (int((x).size()))
#define len(x) (int)x.length()
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define clr(x) (x).clear()
#define uniq(x) x.resize(unique(all(x)) - x.begin());
#define blt(x) __builtin_popcount(x)
#define pb push_back
#define popf pop_front
#define popb pop_back
void print(long long t) {cerr << t;}
void print(int t) {cerr << t;}
void print(string t) {cerr << t;}
void print(char t) {cerr << t;}
void print(double t) {cerr << t;}
void print(long double t) {cerr << t;}
void print(unsigned long long t) {cerr << t;}
template <class T, class V> void print(pair <T, V> p);
template <class T> void print(vector <T> v);
template <class T> void print(set <T> v);
template <class T, class V> void print(map <T, V> v);
template <class T> void print(multiset <T> v);
template <class T, class V> void print(T v[],V n) {cerr << "["; for(int i = 0; i < n; i++) {print(v[i]); cerr << " "; } cerr << "]";}
template <class T, class V> void print(pair <T, V> p) {cerr << "{"; print(p.first); cerr << ","; print(p.second); cerr << "}";}
template <class T> void print(vector <T> v) {cerr << "[ "; for (T i : v) {print(i); cerr << " ";} cerr << "]";}
template <class T> void print(deque <T> v) {cerr << "[ "; for (T i : v) {print(i); cerr << " ";} cerr << "]";}
template <class T> void print(set <T> v) {cerr << "[ "; for (T i : v) {print(i); cerr << " ";} cerr << "]";}
template <class T> void print(multiset <T> v) {cerr << "[ "; for (T i : v) {print(i); cerr << " ";} cerr << "]";}
template <class T, class V> void print(map <T, V> v) {cerr << "[ "; for (auto i : v) {print(i); cerr << " ";} cerr << "]";}
#include <ext/pb_ds/assoc_container.hpp>
using namespace __gnu_pbds;
#define nl '\n'
// for grid problems
int dx[8] = {-1,0,1,0,1,-1,1,-1};
int dy[8] = {0,1,0,-1,1,1,-1,-1};
// lowest / (1 << 17) >= 1e5 / (1 << 18) >= 2e5 / (1 << 21) >= 1e6
void fastIO() {
ios_base::sync_with_stdio(false);
cin.tie(nullptr); cout.tie(nullptr);
}
// file in/out
void setIO(string str = "") {
fastIO();
if (str != "") {
freopen((str + ".in").c_str(), "r", stdin);
freopen((str + ".out").c_str(), "w", stdout);
}
}
// Indexed Set
template <class T> using Tree = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
const long double inf = 1e15;
const int N = 1e2 + 10;
long double dp[N][N][N];
int n, k;
void solve_() {
cin >> n >> k;
vector<pair<long double, long double>> vec;
for(int i = 1; i <= n; i++) {
long double a, b; cin >> a >> b;
vec.emplace_back(b, a);
}
sort(all(vec));
if(n <= 100) {
long double pi = inf;
for(int qq = 0; qq <= n; qq++) {
long double ci = qq + 1;
for(int i = 0; i <= n; i++) {
for(int j = 0; j <= n; j++) {
for(int e = 0; e <= n; e++) {
dp[i][j][e] = inf;
}
}
}
dp[0][0][0] = 0;
for(int i = 0; i < n; i++) {
for(int j = 0; j <= qq; j++) {
for(int e = 0; e <= n && e + j <= i; e++) {
if(j + 1 <= qq && vec[i].first != -1) {
long double qn = j + 1;
dp[i + 1][j + 1][e] = min(dp[i + 1][j + 1][e], dp[i][j][e] + vec[i].first / qn);
}
dp[i + 1][j][e + 1] = min(dp[i + 1][j][e + 1], dp[i][j][e] + vec[i].second / ci);
dp[i + 1][j][e] = min(dp[i + 1][j][e], dp[i][j][e]);
// dbg(dp[i + 1][j][e + 1])
}
}
}
// dbg(dp[n][qq][k])
// for(int i = 0; i <= n; i++) {
// dbg(make_pair(qq, i))
// dbg(dp[n][qq][i])
// }
pi = min(pi, dp[n][qq][max(0, k - qq)]);
}
cout << setprecision(15) << pi << '\n';
return;
}
long double p = inf;
for(int i = 0; i <= n; i++) {
long double cnt = 1, ans = 0;
vector<long double> vi;
int cc = 0;
for(int j = 0; j < i; j++) {
if(vec[j].first == -1) {
vi.push_back(vec[j].second);
continue;
}
cc++;
ans += vec[j].first / cnt;
cnt += 1;
}
for(int j = i; j < n; j++) {
vi.push_back(vec[j].second);
}
sort(all(vi));
int it = 0, mm = k - cc;
while(mm > 0) {
ans += vi[it] / cnt;
it++, mm--;
}
p = min(p, ans);
}
cout << setprecision(15) << p << '\n';
}
int main() {
setIO();
auto solve = [&](int test_case)-> void {
while(test_case--) {
solve_();
}
};
int test_cases = 1;
// cin >> test_cases;
solve(test_cases);
return 0;
}
