This submission is migrated from previous version of oj.uz, which used different machine for grading. This submission may have different result if resubmitted.
#include <bits/stdc++.h>
#define Loop(x,l,r) for (ll x = (l); x < (ll)(r); ++x)
#define LoopR(x,l,r) for (ll x = (r)-1; x >= (ll)(l); --x)
typedef long long ll;
typedef std::pair<int, int> pii;
typedef std::pair<ll , ll > pll;
using namespace std;
const ll inf = 1e15;
int main()
{
	cin.tie(0) -> sync_with_stdio(false);
	int n, k;
	cin >> n >> k;
	vector<pll> a(n);
	Loop (i,0,n) {
		cin >> a[i].second >> a[i].first;
		if (a[i].first == -1)
			a[i].first = inf;
	}
	double ans = inf;
	Loop (cnt,0,k) {
		ll c = 1;
		double sum = 0;
		sort(a.begin(), a.end());
		if (cnt && a[cnt-1].first == inf)
			continue;
		Loop (i,0,cnt) {
			sum += (double)a[i].first / c;
			c++;
		}
		sort(a.begin() + cnt, a.end(), [](pll x, pll y) {
			return x.second < y.second;
		});
		Loop (i,cnt,k)
			sum += (double)a[i].second / c;
		ans = min(ans, sum);
	}
	cout << fixed << setprecision(9);
	cout << ans << '\n';
}
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