// author : thembululquaUwU
// 3.9.2024

#include <bits/stdc++.h>
#define pb push_back
#define fi first
#define se second
#define endl '\n'

using namespace std;
using ll = long long;
using ii = pair <int, int>;
using vi = vector <int>;

const int N = 5e2 + 5;
const int mod = 1e9 + 7;

int n, k;
pair <int, int> state[N];

namespace subtask1{
    const int sub = 105;

    using lb = long double;

    const lb inf = 1e9;

    lb dp[sub][sub][sub];

    void solve(){

        lb ans = inf;

        for (int fix = 0; fix < k; ++ fix){
            for (int i = 0; i <= fix; ++ i){
                for (int j = 0; j <= k - fix; ++ j) dp[0][i][j] = inf;
            }
            dp[0][0][0] = 0;
            for (int i = 1; i <= n; ++ i){
                lb a = state[i].se, b = state[i].fi;
                for (int j = 0; j <= fix; ++ j){
                    for (int t = 0; t <= k - fix; ++ t){
                        dp[i][j][t] = dp[i - 1][j][t];
                        if (t) dp[i][j][t] = min(dp[i][j][t], dp[i - 1][j][t - 1] + a / (fix + 1));
                        if (j && b != -1) dp[i][j][t] = min(dp[i][j][t], dp[i - 1][j - 1][t] + b / j);
                    }
                }
            }

            ans = min(ans, dp[n][fix][k - fix]);
        }

        cout << fixed << setprecision(10) << ans;
    }
}

namespace ac{

    using lb = long double;

    const lb inf = 1e9;

    lb dp[N][N];

    void solve(){

        lb ans = inf;

        for (int fix = 0; fix < k; ++ fix){
            for (int i = 0; i <= n; ++ i)
                for (int j = 0; j <= k; ++ j) dp[i][j] = inf;
            dp[0][0] = 0;
            for (int i = 1; i <= n; ++ i){
                lb a = state[i].se, b = state[i].fi;
                for (int j = 0; j <= min(k, i); ++ j){
                    if (j <= fix){
                        if (j < fix) dp[i][j] = dp[i - 1][j] + a / (fix + 1);
                        if (j && state[i].fi != mod) {
                            dp[i][j] = min(dp[i][j], dp[i - 1][j - 1] + b / j);
                            if (j == fix) dp[i][i] = min(dp[i][i], dp[i][j]);
                        }
                    }
                    else {
                        dp[i][j] = min({dp[i][j], dp[i - 1][j], dp[i - 1][j - 1] + a / (fix + 1)});
                    }
                }
            }

            ans = min(ans, dp[n][k]);
        }

        cout << fixed << setprecision(10) << ans;
    }
}

void solve(){
    cin >> n >> k;
    for (int i = 1; i <= n; ++ i){
        cin >> state[i].se >> state[i].fi;
        if (state[i].fi == -1) state[i].fi = mod;
    }

    sort(state + 1, state + n + 1);

    ac::solve();

    //if (n <= 100) subtask1::solve();
    //else ac::solve();
}

int main(){
    ios_base::sync_with_stdio(0);
    cin.tie(0); cout.tie(0);

    int t = 1; // cin >> t;
    while (t --) solve();
    return 0;
}