#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define int ll
using P = pair<int, int>;
#define all(x) x.begin(), x.end()
#define rep(x,s,e) for (auto x=(s)-((s)>(e));x!=(e)-((s)>(e));((s)<(e)?x++:x--))
#define sz(x) (int)x.size()
const char nl = '\n';
const int mod = 998244353;
bool cmp(P a, P b) {
if (a.second != -1 && b.second != -1)return a.first < b.first;
else if (a.second != -1)return 0;
else if (b.second != -1)return 1;
return a.first < b.first;
}
void solve() {
int n, k; cin >> n >> k;
vector<int> a, b;
rep(i, 0, n) {
int x, y; cin >> x >> y;
if (y != -1)b.push_back(y);
else a.push_back(x);
}
sort(all(a));
sort(all(b));
//for (auto &i: a)cin >> i.first >> i.second;
//cout << sz(a) << nl;
//sort(all(a), cmp);
double res = -1;
rep(i, 0, min(sz(b), k)+1) {
if (k-i > sz(a))continue;
int cnt = 1;
double sm = 0;
rep(j, 0, i) {
sm += (double)(b[j])/double(cnt);
cnt += 1;
}
rep(j, 0, k-i)
sm += (double)(a[j])/double(cnt);
if (res != -1)res = min(res, sm);
else res = sm;
}
//double res = 0;
//int cnt = 1;
//rep(i, 0, n) {
//res += (double)(a[i].first/cnt);
//if (a[i].second != -1)cnt += 1;
//}
cout << res << nl;
}
int32_t main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
solve();
return 0;
}
