#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#define ordered_set tree<int, null_type,less<int>, rb_tree_tag,tree_order_statistics_node_update>
using namespace __gnu_pbds;
using namespace std;
#define pb push_back
#define st first
#define nd second
typedef long long ll;
typedef long double ld;
const ll I = 1000'000'000'000'000'000LL;
const int II = 2'000'000'000;
const ll M = 1000'000'007LL;
const int N = 503;
pair<int, int> tab[N];
ld dp[N][N], dp2[N][N];
ld LiczDP(int n, int k, int l)
{
//cout << fixed << setprecision(7) << "DP: " << l << "\n";
for(int i = 0; i <= n; ++i)
for(int j = 0; j <= k; ++j)
{dp[i][j] = II; dp2[i][j] = II;}
dp[0][0] = 0;
for(int i = 1; i <= n; ++i)
for(int j = 0; j <= l; ++j)
{
dp[i][j] = dp[i - 1][j] + (ld)tab[i].nd / (ld)(l + 1);
if(j > 0)
dp[i][j] = min(dp[i][j], dp[i - 1][j - 1] + (ld)tab[i].st / (ld)j);
//cout << i << " " << j << " " << dp[i][j] << "\n";
}
for(int i = l; i <= n; ++i)
{
dp2[i][i - l] = dp[i][l];
//cout << "C: " << i << " " << dp2[i][k - l] << "\n";
for(int j = 0; j <= k - l && i > 0; ++j)
{
dp2[i][j] = min(dp2[i][j], dp2[i - 1][j]);
if(j > 0)
dp2[i][j] = min(dp2[i][j], dp2[i - 1][j - 1] + (ld)tab[i].nd / (ld)(l + 1));
}
//cout << "C: " << i << " " << dp2[i][k - l] << "\n";
}
return dp2[n][k - l];
}
void Solve()
{
cout << fixed << setprecision(7);
int n, k;
cin >> n >> k;
for(int i = 1; i <= n; ++i)
{
cin >> tab[i].nd >> tab[i].st;
if(tab[i].st == -1) tab[i].st = II;
}
sort(tab + 1, tab + 1 + n);
ld ans = II;
//cout << "T:\n";
//for(int i = 1; i <= n; ++i)
//cout << tab[i].st << " " << tab[i].nd << "\n";
for(int i = 0; i < k; ++i)
ans = min(ans, LiczDP(n, k, i));
cout << fixed << setprecision(7) << ans << "\n";
}
int main()
{
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
//int t; cin >> t;
//while(t--)
Solve();
return 0;
}
