#include <bits/stdc++.h>
using namespace std;
#define int long long
#define intd long double
#define debug(x) cout << '|' << x << '|' << '\n';
#define debug2(x, y) cout << x << " | " << y << '\n';
#define debug3(x, y, z) cout << x << " | " << y << " | " << z << '\n';
deque<pair<int, int>> v;
intd memo[510][510];
vector<int> precomp;
int N, K, intendedA;
intd dp(int idx, int sizeOfA) {
if (memo[idx][sizeOfA] != 0) return memo[idx][sizeOfA];
if (idx == N) return (sizeOfA == intendedA ? 0 : 1e18);
intd res = 1e18;
int sizeOfB = K - intendedA + 1;
if (sizeOfA == intendedA && sizeOfB == 1) return 0;
// take B
if (idx < v.size() && v[idx].first != -1) {
if (idx - sizeOfA + 1 >= sizeOfB) {
res = min(res, dp(idx + 1, sizeOfA));
// cout << idx << " " << sizeOfA << " " << "DON'T TAKE ANYTHING: " << dp(idx + 1, sizeOfA) << endl;
}
else {
res = min(res, dp(idx + 1, sizeOfA) + (intd)v[idx].first / (intd)(idx - sizeOfA + 1));
// cout << idx << " " << sizeOfA << " " << "TAKE B: " << dp(idx + 1, sizeOfA) + (intd)v[idx].first / (intd)(idx - sizeOfA + 1) << endl;
}
}
// take A
if (idx < v.size() && sizeOfA < intendedA) {
res = min(res, dp(idx + 1, sizeOfA + 1) + (intd)v[idx].second / (intd)sizeOfB);
// cout << idx << " " << sizeOfA << " " << "TAKE A: " << dp(idx + 1, sizeOfA + 1) + (intd)v[idx].second / (intd)sizeOfB << endl;
}
// take remainder of A
if (sizeOfA < intendedA && intendedA - sizeOfA - 1 < precomp.size() && (idx - sizeOfA) >= sizeOfB - 1) {
res = min(res, (intd)precomp[intendedA - sizeOfA - 1] / (intd)sizeOfB);
// cout << idx << " " << sizeOfA << " TAKE REMAINDER OF A: " << (intd)precomp[intendedA - sizeOfA - 1] / (intd)sizeOfB << endl;
}
memo[idx][sizeOfA] = res;
return res;
}
bool cmp(pair<int, int> a, pair<int, int> b) {
if ((a.first == -1 && b.first == -1) || (a.first != -1 && b.first != -1)) {
if (a.first != b.first) return a.first < b.first;
return a.second < b.second;
}
if (b.first == -1) return true;
return false;
}
int32_t main() {
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cout.tie(NULL);
cin >> N >> K;
for (int i = 0; i < N; i++) {
int A, B;
cin >> A >> B;
v.push_back(make_pair(B, A));
}
sort(v.begin(), v.end(), cmp);
// for (auto i : v) cout << i.first << " " << i.second << endl;
for (int i = 0; i < N; i++) {
if (v[i].first == -1) {
if (precomp.empty()) precomp.push_back(v[i].second);
else precomp.push_back(precomp.back() + v[i].second);
}
}
for (int i = N - 1; i >= 0; i--) {
if (v[i].first == -1) v.pop_back();
}
// for (auto i : precomp) cout << i << endl;
cout << fixed << setprecision(15);
intd res = 1e18;
for (int i = 0; i <= K; i++) {
intendedA = i;
memset(memo, 0, sizeof memo);
// cout << intendedA << endl;
res = min(res, dp(0, 0));
}
cout << res;
}
