#include <bits/stdc++.h>
#define int long long
using namespace std;
using ld = long double;
const int MAXN = 510;
const ld INF = 1e9;
struct state{
ld a, b; int i;
bool operator < (state other){
if(b != other.b) return b < other.b;
if(a != other.a) return a > other.a;
return i < other.i;
}
} s[MAXN];
int n, k;
ld solve(int i){
ld sum_a = 0;
vector<int> A;
for(int j=(i + 1); j<=n; j++){
A.push_back(s[j].a);
}
sort(A.begin(), A.end());
for(int j=0; j<k-i; j++) sum_a += A[j];
ld ans = INF;
ld sum_b = 0;
for(int j=1; j<=i; j++){
if(s[j].b == INF) return INF;
sum_b += s[j].b / j;
ld cur_ans = 0;
for(int k=(j + 1); k<=i; k++){
cur_ans += s[k].a / (k - j);
}
if(j == i) cur_ans = max(cur_ans, sum_a / (j + 1));
else cur_ans = max(cur_ans, sum_a / j);
ans = min(ans, cur_ans + sum_b);
}
return ans;
}
int32_t main(){
cin.tie(0)->sync_with_stdio(0);
cin >> n >> k;
ld ans = 0;
for(int i=1; i<=n; i++){
cin >> s[i].a >> s[i].b;
s[i].i = i;
if(s[i].b == -1) s[i].b = INF;
ans += s[i].a;
}
sort(s + 1, s + n + 1);
for(int i=1; i<=k; i++){
ans = min(ans, solve(i));
}
cout << fixed << setprecision(10) << ans << "\n";
return 0;
}
