#include <bits/stdc++.h>
#define pb push_back
#define f first
#define sc second
using namespace std;
typedef long long int ll;
typedef string str;
typedef double ld;
int main(){
ios_base::sync_with_stdio(0);
cin.tie(0);
cerr.precision(100);
cout.precision(100);
int n, k; cin >> n >> k;
vector<pair<int, int>> v(n);
for(auto &p: v) cin >> p.f >> p.sc;
sort(v.begin(), v.end(), [](pair<ld, ld> a, pair<ld, ld> b){
swap(a.f, a.sc);
swap(b.f, b.sc);
if(a.f == -1) a.f = 1e9;
if(b.f == -1) b.f = 1e9;
return a < b;
});
vector<vector<ld>> last(n, vector<ld>(n+1, 1e6));
for(int i = 0; i < n; i++) last[i][0] = 0;
for(int c = 1; c <= n; c++){
priority_queue<int> pq;
int s = 0;
for(int i = n-1; i >= n-c; i--) pq.push(v[i].f), s+=v[i].f;
last[n-c][c] = s;
for(int i = n-c-1; i >= 0; i--){
if(v[i].f < pq.top()) s-=pq.top(), pq.pop(), pq.push(v[i].f), s+=v[i].f;
last[i][c] = s;
}
}
ld ans = last[0][k];
for(int c = 0; c <= k; c++){
vector<vector<ld>> dp(n, vector<ld>(c+1, 1e6));
for(int i = 0; i < n; i++){
for(int j = 0; j <= min(i+1, c); j++){
if(i == 0){
if(j == 0) dp[i][j] = ld(v[i].f)/ld(c+1);
else if(j == 1 && v[i].sc != -1) dp[i][j] = v[i].sc;
continue;
}
if(i >= j)
dp[i][j] = min(dp[i][j], dp[i-1][j]+ld(v[i].f)/ld(c+1));
if(v[i].sc != -1 && j > 0)
dp[i][j] = min(dp[i][j], dp[i-1][j-1]+ld(v[i].sc)/ld(j));
}
}
for(int i = 0; i < k; i++)
ans = min(ans, dp[i][c] + (i == n-1 ? 0.0 : last[i+1][k-i-1]/ld(c+1)));
}
cout << ans << "\n";
}
