#include <bits/stdc++.h>
using namespace std;
using ld = long double;
#define int long long
int n,k;
ld m;
pair<ld,ld> a[505];
ld dp[505][505];
ld solve()
{
///daca sortez dupa b, mi-e foarte ez
///dp[i][j] = costul minim sa ajung la omul i sa fi luat j a-uri
///c = min(m + 1,i - j + 1)
///dp[i][j] -> dp[i + 1][j] de cost b[i + 1] / c ofc daca n-am luat prea multe b-uri
///dp[i][j] -> dp[i + 1][j + 1] de cost a[i + 1] / m
for (int i = 0; i <= n; i++)
{
for (int j = 0; j <= n; j++)
dp[i][j] = 1e9;
}
dp[0][0] = 0;
for (int i = 1; i <= n; i++)
{
for (int j = 0; j <= i; j++)
{
ld c = i - j;
//if (i - j <= m)
if (i - j <= m and i - j != 0)
dp[i][j] = min(dp[i][j],dp[i - 1][j] + a[i].first / c);
else if (i - j > m)
dp[i][j] = min(dp[i][j],dp[i - 1][j]);
if (j >= 1)
dp[i][j] = min(dp[i][j],dp[i - 1][j - 1] + a[i].second / (m + 1));
//cout << i << ' ' << j << ' ' << dp[i][j] << endl;
}
}
//cout << dp[n][(int)(k - m)] << endl;
return dp[n][(int)(k - m)];
}
ld slv(ld x)
{
m = x;
return solve();
}
ld solve_normal()
{
///fuckkkk n-a mers greedy-ul :facepalm:
sort(a + 1,a + n + 1);
ld ans = 1e6;
//for (m = 0; m < k; m++)
// ans = min(ans,solve());
int st = 0,pas = 1 << 8;
while (pas != 0)
{
if (st + pas < k and slv(st + pas - 1) > slv(st + pas))
st += pas;
pas /= 2;
}
ans = slv(st);
return ans;
}
/*ld solve_brut()
{
ld ans = 1e6;
vector<int>ids;
for (int i = 1; i <= n; i++)
ids.push_back(i);
do
{
for (ld m = 1; m <= k; m++)
{
ld cur = 0;
for (ld j = 1; j < m; j++)
cur += b[ids[j - 1]] / j;
for (ld j = m; j <= k; j++)
cur += a[ids[j - 1]] / m;
ans = min(ans,cur);
}
}while(next_permutation(ids.begin(),ids.end()));
return ans;
}*/
bool generez_teste = false;
void citire()
{
if (generez_teste == false)
{
cin >> n >> k;
for (int i = 1; i <= n; i++)
cin >> a[i].second >> a[i].first;
for (int i = 1; i <= n; i++)
if (a[i].first == -1)
a[i].first = 1e9;
}
/*else
{
n = 3;
k = 2;
for (int i = 1; i <= n; i++)
{
a[i] = 1 + rand() % 9;
b[i] = a[i] + rand() % 10;
if (b[i] - a[i] == 9)
b[i] = -1;
if (b[i] == -1)
b[i] = 1e9;
}
}*/
}
signed main()
{
cout << setprecision(5) << fixed;
citire();
cout << solve_normal();
return 0;
/*srand(0);
ld ans_normal,ans_brut;
while (true)
{
citire();
ans_normal = solve_normal();
ans_brut = solve_brut();
if (abs(ans_normal - ans_brut) >= 0.00001d)
{
for (int i = 1; i <= n; i++)
cout << a[i] << ' ' << b[i] << endl;
break;
}
}
cout << setprecision(5) << fixed;
//cout << ans_normal << ' ' << ans_brut;
return 0;*/
}
/**
3
3
9 9
3 6
7 14
**/
