#include <bits/stdc++.h>
#pragma GCC optimize("O3,unroll-loops")
#pragma GCC target("avx2")
#define int long long
#define pii pair<int,int>
#define vi vector<int>
#define ff first
#define ss second
#define sp << " " <<
#define all(x) x.begin(),x.end()
#define big(x) ((int)(x.size()))
using namespace std;
const int MOD = 1e9+7, LIM = 1e6+1, inf = 2e18;
const int N = 1e5+1;
void solve() {
int n,k;
cin >> n >> k;
vector<pair<double,double>> ps(n+1);
for (int i=1;i<=n;i++) {
cin >> ps[i].ff >> ps[i].ss;
if (ps[i].ss == -1) ps[i].ss = 1e18;
}
sort(1+all(ps),[&](pii p1,pii p2){
return pii{p1.ss,p1.ff} < pii{p2.ss,p2.ff};
});
double ans = inf;
double dp[n+1][n+1];
for (int c = 0;c < k;c++) {
for (int i = 0;i<=n;i++) for (int j = 0;j<=n;j++) dp[i][j] = inf;
dp[0][0] = 0;
for (int i = 0;i<=n;i++) {
for (int j = 0;j<=n;j++) {
if (dp[i][j] == inf) continue;
int j2 = min(c,i-j);
if (j2 < 0) continue;
if (j+j2 == k && j2 == c) ans = min(ans,dp[i][j]);
if (i == n) continue;
dp[i+1][j+1] = min(dp[i+1][j+1],dp[i][j]+ps[i+1].ff/(c+1));
dp[i+1][j] = min(dp[i+1][j],dp[i][j]+(j2!=c)*(ps[i+1].ss/(j2+1)));
}
}
}
cout << fixed << setprecision(16) << ans << '\n';
}
signed main() {
ios_base::sync_with_stdio(0); cin.tie(0);
int t = 1;
//cin >> t;
while (t --> 0) solve();
}
