#include <bits/stdc++.h>
#define ll long long
using namespace std;
int main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
ll n,k;
cin >> n >> k;
vector<pair<ll,ll>> ab(n);
vector<pair<ll,ll>> a,b;
for (int i=0; i<n; i++) {
cin >> ab[i].second >> ab[i].first;
if (ab[i].first==-1) b.push_back(ab[i]);
else a.push_back(ab[i]);
}
sort(a.begin(), a.end());
sort(b.begin(), b.end());
for (auto i : b) {
a.push_back(i);
}
vector<vector<double>> s(n+1, vector<double>(n+1));
for (int i=0; i<=n; i++) {
vector<ll> v;
for (int j=i; j<n; j++) {
v.push_back(a[j].second);
}
sort(v.begin(), v.end());
double s1 = 0;
s[i][0] = 0;
for (int j=1; j<=v.size(); j++) {
s1+=v[j-1];
s[i][j] = s1;
}
}
double res = 1e18;
for (int c=0; c<=k; c++) {
vector<vector<double>> dp(n+1, vector<double>(c+1, 1e18));
dp[0][0] = 0;
for (int i=1; i<=k; i++) {
for (int j=0; j<=c; j++) {
if (dp[i-1][j]!=1e18) dp[i][j] = min(dp[i][j], dp[i-1][j]+(double)a[i-1].second/(c+1));
if (j>0 && dp[i-1][j-1]!=1e18 && a[i-1].first!=-1) dp[i][j] = min(dp[i][j], dp[i-1][j-1]+(double)a[i-1].first/j);
}
if (dp[i][c]!=1e18) {
res = min(res, dp[i][c]+s[i][k-i]/(c+1));
}
}
if (c==0) res = min(res, s[0][k]);
}
cout << fixed << setprecision(15) << res;
}
