#include <bits/stdc++.h>
using namespace std;
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
#define pb push_back
#define ff first
#define ss second
#define all(x) x.begin(),x.end()
#define rall(x) x.rbegin(),x.rend()
#define ordered_set tree<int, null_type,less<int>, rb_tree_tag,tree_order_statistics_node_update>
#define int long long
#define double long double
const int N = 1e6+5, inf = 1e9, mod = 1e9+7;
template <class F, class _S>
bool chmin(F &u, const _S &v){
bool flag = false;
if ( u > v ){
u = v; flag |= true;
}
return flag;
}
template <class F, class _S>
bool chmax(F &u, const _S &v){
bool flag = false;
if ( u < v ){
u = v; flag |= true;
}
return flag;
}
double dp[505][505];
void solve(){
int n, k;cin >> n >> k;
vector<pair<int,int> > v;
for(int i = 0; i < n; i++){
int a, b;
cin >> a >> b;
if(b == -1)b = inf;
v.pb({b, a});
}
sort(all(v));
vector<int> a(n+1), b(n+1);
for(int i = 1; i <= n; i++){
b[i] = v[i-1].ff;
a[i] = v[i-1].ss;
}
vector<int> _a;
for(int i = 1; i <= n; i++)_a.pb(a[i]);
sort(all(_a));
double ans = 0;
for(int i = 0; i < k; i++)ans+=_a[i];
for(int m = 1; m <= k; m++){
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 = 1; i <= k; i++){
for(int j = 0; j <= min(i, m); j++){
if(j && b[i] < inf)chmin(dp[i][j], dp[i-1][j-1] + (double)b[i]/(double)(j));
chmin(dp[i][j], dp[i-1][j] + (double)a[i]/(double)(m+1));
if(j==m){
vector<int> v;
for(int q = i+1;q <= n; q++)v.pb(a[q]);
sort(all(v));
int sum = 0;
for(int q = 0; q < k-i; q++)sum += v[q];
chmin(ans, dp[i][j] + (double)sum / (double)(m+1));
}
}
}
}
cout << fixed << setprecision(15) << ans << '\n';
}
signed main(){
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
cout.tie(nullptr);
int tt = 1;
//cin >> tt;
while(tt--){
solve();
}
}
