#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef long double ld;
typedef pair<ll,ll> pl;
typedef pair<int,int> pii;
typedef tuple<int,int,int> tt;
#define all(a) a.begin(), a.end()
#define filter(a) a.erase(unique(all(a)), a.end())
const double INF = 1e9;
double dp[505][505];
struct P {
int norm, col;
P() : norm(0), col(0) {}
P (int a, int b) : norm(a), col(b) {}
friend istream& operator >> (istream &inp, P &cur) {
inp >> cur.norm >> cur.col;
return inp;
}
bool operator < (const P &o) const {
if (col == o.col || col == -1) return 0;
if (o.col == -1) return 1;
return col < o.col;
}
} a[505];
int main()
{
ios::sync_with_stdio(0);
cin.tie(0);
int n, k; cin >> n >> k;
for (int i = 1; i <= n; i++) cin >> a[i];
sort(a + 1, a + 1 + n);
for (int i = 0; i <= n; i++)
for (int j = 0; j <= k; j++)
dp[i][j] = INF;
double ans = INF;
for (int cntNorm = 0; cntNorm <= k; cntNorm++) {
int collab = k - cntNorm;
dp[0][0] = 0;
for (int i = 1; i <= n; i++) {
for (int j = 0; j <= min(i, cntNorm); j++) {
//dp[i][j] = dp[i - 1][j];
if (j && dp[i - 1][j - 1] != INF)
dp[i][j] = min(dp[i][j], dp[i - 1][j - 1] + double(a[i].norm) / double(collab + 1));
if (i - j <= collab && dp[i - 1][j] != INF && a[i].col != -1)
dp[i][j] = min(dp[i][j], dp[i - 1][j] + double(a[i].col) / double(i - j));
if (i - j > collab)
dp[i][j] = min(dp[i][j], dp[i - 1][j]);
}
}
//cout << cntNorm << " " << dp[n][cntNorm] << "\n";
ans = min(ans, dp[n][cntNorm]);
for (int i = 1; i <= n; i++)
for (int j = 0; j <= min(i, cntNorm); j++)
dp[i][j] = INF;
}
cout << fixed << setprecision(9) << ans;
return 0;
}
