#include <bits/stdc++.h>
#define int long long
#define pb push_back
#define em emplace_back
#define F(i,x,y) for(int i=x;i<=y;i++)
#define G(i,x,y) for(int i=x;i>=y;i--)
#define W(G,i,x) for(auto&i:G[x])
#define W_(G,i,j,x) for(auto&[i,j]:G[x])
#define add(x,y) z[x].em(y)
#define add_(x,y) add(x,y),add(y,x)
#define Add(x,y,d) z[x].em(y,d)
#define Add_(x,y,z) Add(x,y,z),Add(y,x,z);
#ifdef int
#define inf (7611257611378358090ll/2)
#else
#define inf 0x3f3f3f3f
#endif
using namespace std;
const int N = 3010, mod = 1e9 + 7;
struct Node {
    double a, b;
    bool operator<(const Node &r) const {
        return a < r.a || a == r.a && b < r.b;
    }
} z[N];
double f[N][N], suf[N][N];
auto main() [[O3]] -> signed {
    int n, k;
    cin >> n >> k;
    F(i, 1, n) {
        cin >> z[i].a >> z[i].b;
        if (z[i].b < 0) {
            z[i].b = inf;
        }
    }
    sort(z + 1, z + n + 1);
    G(i, n, 1) {
        vector<Node> v;
        G(j, n, i) {
            v.pb(z[j]);
        }
        sort(v.begin(), v.end());
        F(j, 0, (int)v.size() - 1) {
            suf[i][j + 1] = suf[i][j] + z[j].a;
        }
    }
    F(i, 0, N - 1) {
        F(j, 0, N - 1) {
            f[i][j] = inf;
        }
    }
    f[0][0] = 0;
    double mi = inf;
    F(_, 0, k) {
        F(i, 1, k) {
            F(j, 0, i) {
                if (j) {
                    f[i][j] = min(f[i - 1][j] + 1. * z[i].a / (_ + 1), f[i - 1][j - 1] + z[i].b / j);
                } else {
                    f[i][j] = f[i - 1][j] + 1. * z[i].a / (_ + 1);
                }
                if (j == _) {
                    mi = min(mi, f[i][j] + suf[i + 1][k - i] / (j + 1));
                }
            }
        }
    }
    double tt = min(mi, suf[1][k]);
    printf("%.23lf\n", tt);
}