#include <bits/stdc++.h>
using namespace std;
#define int long long
#define db double
#define MAX 502
db dp[MAX][MAX][MAX];
int n, k;
pair<db, db> info[MAX];
bool cmp(pair<db, db> a, pair<db, db> b){
if (a.second == -1) a.second = 1000000000;
if (b.second == -1) b.second = 1000000000;
return a.second > b.second;
}
db recur(int idx, int colabCount, int voteCount){
if (idx == n && voteCount >= k) return 0;
else if (idx == n) return 1000000000;
if (dp[idx][colabCount][voteCount] != -1) return dp[idx][colabCount][voteCount];
if (info[idx].second == -1) return dp[idx][colabCount][voteCount] = min(recur(idx+1, colabCount, voteCount), recur(idx+1, colabCount, voteCount+1) + info[idx].first/colabCount);
return dp[idx][colabCount][voteCount] = min({recur(idx+1, colabCount, voteCount), recur(idx+1, colabCount, voteCount+1) + info[idx].first/colabCount, recur(idx+1, colabCount+1, voteCount+1) + info[idx].second/colabCount});
}
main(){
cin >> n >> k;
for (int x = 0; x < n; x++) cin >> info[x].first >> info[x].second;
sort(info, info+n);
//for (int x = 0; x < n; x++) cout << info[x].first << ' ' << info[x].second << '\n';
for (int x = 0; x <= n; x++) for (int y = 0; y <= n+1; y++) for (int z = 0; z <= n; z++) dp[x][y][z] = -1;
db ans = 1000000000000000LL;
for (int x = 0; x <= n; x++){
//make use of x colabs
//initial sort is optimal for 0 colabs
vector<pair<db, db>> colabSect;
vector<pair<db, db>> voteSect;
//wait is dp even needed
for (int y = 0; y < n; y++) voteSect.push_back(info[y]);
sort(voteSect.begin(), voteSect.end(), cmp); //give cheapest
for (int y = 0; y < x; y++){
colabSect.push_back(voteSect.back()); voteSect.pop_back();
}
if (colabSect.size() != 0 && colabSect.back().second == -1) break;
sort(voteSect.begin(), voteSect.end()); //return to cheapest votes
int votesNeeded = max(k - (int)colabSect.size(), 0LL);
int colabCount = 1;
db curAns = 0;
for (auto y : colabSect){
curAns += y.second/colabCount; colabCount++;
}
for (int y = 0; y < votesNeeded; y++){
curAns += voteSect[y].first/colabCount;
}
ans = min(curAns, ans);
}
cout << std::setprecision(9) << ans;
}
