#include<bits/stdc++.h>
using namespace std;
#define task "a"
#define se second
#define fi first
#define ll long long
#define ii pair<ll, ll>
const long mxN = 2e5 + 7, inf = 1e9 + 7;
int n, k;
ii a[mxN];
int main()
{
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cout.tie(NULL);
//freopen(task".INP", "r", stdin);
//freopen(task".OUT", "w", stdout);
cin >> n >> k;
for (int i = 1; i <= n; i++)
{
cin >> a[i].se >> a[i].fi;
if (a[i].fi == -1)
a[i].fi = inf;
}
sort(a + 1, a + n + 1);
double sum = 0, ans = inf;
for (int i = 0; i <= k; i++)
{
if (a[i].fi == inf)
break;
if (i)
sum += double(a[i].fi) / i;
vector<double> vc;
for (int j = i + 1; j <= n; j++)
vc.push_back(a[j].se);
sort(vc.begin(), vc.end());
double tmp = 0;
for (int j = 0; j < k - i; j++)
tmp += vc[j] / (i + 1);
ans = min(ans, sum + tmp);
}
cout << fixed << setprecision(9) << ans;
}
