#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using db = double;
const int N = 501;
db dp[N][N]; //id, # of b's
db solved[N];
int main() {
ios::sync_with_stdio(false);
cin.tie(nullptr);
int n, K;
cin >> n >> K;
vector<int> a(n), b(n), ob(n), oa(n);
int cntb = 0;
for (int i = 0; i < n; ++i) {
cin >> a[i] >> b[i];
if (b[i] != -1) {
cntb += 1;
}
}
iota(oa.begin(), oa.end(), 0), iota(ob.begin(), ob.end(), 0);
sort(oa.begin(), oa.end(), [&a](int i, int j) {
return a[i] < a[j];
});
sort(ob.begin(), ob.end(), [&](int i, int j) {
if (b[i] == -1) return false;
if (b[j] == -1) return true;
return b[i] < b[j];
});
const db inf = 1e12;
auto solve = [&](int mx) -> db {
if (solved[mx] == 0) {
for (int i = 0; i <= n; ++i) for (int j = 0; j <= n; ++j) dp[i][j] = inf;
dp[0][0] = 0;
db ans = inf;
vector<bool> used(n);
auto relax = [&](int cnt, db start) {
int done = cnt;
if (done > K) {
return;
}
db now = start;
for (int j: oa) {
if (done < K && !used[j]) {
done += 1;
now += a[j] / db(mx + 1);
}
}
ans = min(ans, now);
};
for (int i = 1; i <= n; ++i) {
int idx = ob[i - 1];
relax(i - 1, dp[i - 1][mx]);
if (b[idx] == -1) {
break;
}
for (int k = 0; k <= min(mx, i); ++k) {
int x = i - k;
if (x < 0 || dp[i - 1][k] == inf || x + k > K) {
continue;
}
dp[i][k] = min(dp[i][k], dp[i - 1][k] + a[idx] / db(mx + 1));
if (k != mx) {
dp[i][k + 1] = min(dp[i][k + 1], dp[i - 1][k] + b[idx] / db(k + 1));
} else {
relax(k + x - 1, dp[i - 1][k]);
}
}
used[idx] = true;
relax(i, dp[i][mx]);
}
solved[mx] = ans;
}
return solved[mx];
};
int r = min(K, cntb);
int x = r / 2;
for (int k = 9; k > -1; --k) {
db ansL = (x >= (1 << k) ? solve(x - (1 << k)) : inf);
db ans = solve(x);
db ansR = (x + (1 << k) <= r ? solve(x + (1 << k)) : inf);
if (ansL <= ans && ansL <= ansR) {
x -= (1 << k);
} else if (ansR <= ans) {
x += (1 << k);
}
}
cout << fixed << setprecision(3) << solve(x);
return 0;
}
