// Success consists of going from failure to failure without loss of enthusiasm
#include <bits/stdc++.h>
using namespace std;
#define nl '\n'
#define sz(x) int(x.size())
#define pb push_back
#define f first
#define s second
#define mp make_pair
using pi = pair<int, int>;
template<class T> using V = vector<T>;
using vi = V<int>;
using vpi = V<pi>;
using db = double;
const int BIG = 1e8;
const db INF = 1e9;
const db eps = 1e-5;
int main() {
cin.tie(0)->sync_with_stdio(0);
int N, K; cin >> N >> K;
vpi A(N); for(auto& x : A) {
cin >> x.s >> x.f;
if (x.f == -1) x.f = BIG;
}
sort(begin(A), end(A));
db ans = INF;
for(int x = 0; x <= K; x++) {
V<V<db>> dp(x + 1, V<db>(2, INF)); // dp[have][ok]
dp[0][x == K] = 0;
for(int i = 0; i < N; i++) {
V<V<db>> ndp(x + 1, V<db>(2, INF));
for(int have = 0; have <= x; have++) for(int ok = 0; ok < 2; ok++) {
// take i as vote
if (have + 1 <= x) {
ndp[have + 1][ok] = min(ndp[have + 1][ok], dp[have][ok] + db(A[i].s) / db(K - x + 1));
}
// take i as collaborator
if (!ok) {
if (A[i].f != BIG) {
int c = i + 1 - have, nok = c == (K - x);
// cout << dp[have][ok] << " " << c << " " << A[i].f << " " << db(A[i].f) / db(c) << endl;
ndp[have][nok] = min(ndp[have][nok], dp[have][ok] + db(A[i].f) / db(c));
}
} else ndp[have][ok] = min(ndp[have][ok], dp[have][ok]);
}
dp.swap(ndp);
}
if (ans < dp[x][1]) break;
ans = dp[x][1];
}
cout << fixed << setprecision(15);
cout << ans << nl;
exit(0-0);
}
// Breathe In, Breathe Out
