/** - dwuy -
／＞ フ
| _ _|
／`ミ _x ノ
/ |
/ ヽ ?
／￣| | | |
| (￣ヽ＿_ヽ_)_)
＼二つ
**/
#include <bits/stdc++.h>
#define fastIO ios_base::sync_with_stdio(false); cin.tie(NULL)
#define file(a) freopen(a".inp","r",stdin); freopen(a".out", "w",stdout)
#define fi first
#define se second
#define endl "\n"
#define len(s) (int)((s).size())
#define MASK(k)(1LL<<(k))
#define TASK "test"
#define int long long
using namespace std;
typedef tuple<int, int, int> tpiii;
typedef pair<double, double> pdd;
typedef pair<int, int> pii;
typedef long long ll;
const long long OO = 1e18;
const int MOD = 1e9 + 7;
const int INF = 1e9;
const int MX = 505;
int n, k;
pii a[MX];
int32_t main(){
fastIO;
//file(TASK);
cin >> n >> k;
for(int i=1; i<=n; i++){
cin >> a[i].fi >> a[i].se;
if(a[i].se == -1) a[i].se = OO;
}
sort(a + 1, a + 1 + n, [](const pii &a, const pii &b) -> bool {return a.se < b.se;});
double ans = 1e18;
double cur = 0;
for(int i=0; i<=n; i++) if(a[i].se != OO){
cur += i? 1.0*a[i].se/i : 0;
vector<int> vt;
for(int j=i+1; j<=n; j++){
vt.push_back(a[j].fi);
}
sort(vt.begin(), vt.end());
double tmp = 0;
for(int j=0; j<k-i; j++) tmp += 1.0*vt[j]/(i + 1);
ans = min(ans, cur + tmp);
}
cout << setprecision(7) << fixed << ans << endl;
return 0;
}
