// author : thembululquaUwU
// 3.9.2024
#include <bits/stdc++.h>
#define pb push_back
#define fi first
#define se second
#define endl '\n'
using namespace std;
using ll = long long;
using ii = pair <int, int>;
using vi = vector <int>;
const int N = 5e2 + 5;
const int mod = 1e9 + 7;
int n, k;
pair <int, int> state[N];
namespace subtask1{
const int sub = 105;
using lb = long double;
const lb inf = 1e9;
lb dp[sub][sub][sub];
void solve(){
lb ans = inf;
for (int fix = 0; fix < k; ++ fix){
for (int i = 0; i <= fix; ++ i){
for (int j = 0; j <= k - fix; ++ j) dp[0][i][j] = inf;
}
dp[0][0][0] = 0;
for (int i = 1; i <= n; ++ i){
lb a = state[i].se, b = state[i].fi;
for (int j = 0; j <= fix; ++ j){
for (int t = 0; t <= k - fix; ++ t){
dp[i][j][t] = dp[i - 1][j][t];
if (t) dp[i][j][t] = min(dp[i][j][t], dp[i - 1][j][t - 1] + a / (fix + 1));
if (j && b != -1) dp[i][j][t] = min(dp[i][j][t], dp[i - 1][j - 1][t] + b / j);
}
}
}
ans = min(ans, dp[n][fix][k - fix]);
}
cout << fixed << setprecision(10) << ans;
}
}
namespace ac{
using lb = long double;
const lb inf = 1e9;
lb dp[N][N];
void solve(){
lb ans = inf;
for (int fix = 0; fix < k; ++ fix){
for (int i = 0; i <= n; ++ i)
for (int j = 1; j <= k; ++ j) dp[i][j] = inf;
dp[0][0] = 0;
for (int i = 1; i <= n; ++ i){
lb a = state[i].se, b = state[i].fi;
for (int j = 0; j <= min(k, i); ++ j){
if (j <= fix){
dp[i][j] = dp[i - 1][j] + a / (fix + 1);
if (j && state[i].fi != mod) {
dp[i][j] = min(dp[i][j], dp[i - 1][j - 1] + b / j);
if (j == fix) dp[i][i] = dp[i][j];
}
}
else {
dp[i][j] = min({dp[i][j], dp[i - 1][j], dp[i - 1][j - 1] + a / (fix + 1)});
}
}
}
ans = min(ans, dp[n][k]);
}
cout << fixed << setprecision(10) << ans;
}
}
void solve(){
cin >> n >> k;
for (int i = 1; i <= n; ++ i){
cin >> state[i].se >> state[i].fi;
if (state[i].fi == -1) state[i].fi = mod;
}
sort(state + 1, state + n + 1);
ac::solve();
//if (n <= 100) subtask1::solve();
//else ac::solve();
}
int main(){
ios_base::sync_with_stdio(0);
cin.tie(0); cout.tie(0);
int t = 1; // cin >> t;
while (t --) solve();
return 0;
}
