#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define ld long double
const bool Multitest = 0;
const int N = 505; const ll offset = 1e9;
int n, k;
struct Type
{
ld x, y;
}; Type a[N];
bool cmp1(Type a, Type b)
{
return a.y < b.y;
}
bool cmp2(Type a, Type b)
{
return a.x < b.x;
}
void work()
{
cin >> n >> k;
for(int i = 1 ; i <= n ; i++)
{
cin >> a[i].x >> a[i].y;
if(a[i].y == -1) a[i].y = 1e9;
}
sort(a + 1, a + 1 + n, cmp1);
ld ans = 1e18, t = 0;
for(int i = 0 ; i <= k ; i++)
{
if(i != 0)
{
t += a[i].y / i;
}
vector<Type> b;
for(int j = i + 1 ; j <= n ; j++) b.push_back(a[j]);
sort(b.begin(), b.end(), cmp2);
// for(auto x : b)
// {
// cout << x.x << ' ' << x.y << '\n';
// }
ld at = 0;
for(int x = 0 ; i + x < k ; x++)
{
at += b[x].x / (i + 1);
}
ans = min(ans, t + at);
}
cout << setprecision(9) << fixed << (1.0 * ans);
}
int main()
{
ios_base::sync_with_stdio(false);
cin.tie(0); cout.tie(0);
int q = 1;
if(Multitest) cin >> q;
while(q--) work();
}
