#include <bits/stdc++.h>
using namespace std;
void fastIO(){ios_base::sync_with_stdio(false),cin.tie(0);}
#define int long long
#define ld long double
const int INF = (int)1e18;
int N, K;
struct Val{int vote, colab;};
bool cmpVal (const Val& a, const Val& b) {
if (a.colab == -1) return false;
else if (b.colab == -1) return true;
else return tie(a.colab, a.vote) < tie(b.colab, b.vote);
}
vector<Val> vals;
ld ans = (ld)INF;
struct Segtree {
int numleaves;
vector<int> numVals, sumVals;
Segtree (int n) {
numleaves = 1;
while (numleaves < n) numleaves *= 2;
numVals.assign(2*numleaves, 0);
sumVals.assign(2*numleaves, 0);
}
int query (int x) {
int node = 1;
int numBef = 0, sumBef = 0;
while (numleaves > node) {
if (numBef + numVals[2*node] >= x) {
node = 2*node;
}
else {
numBef += numVals[2*node];
sumBef += sumVals[2*node];
node = 2*node+1;
}
}
sumBef += (x-numBef)*(node-numleaves);
return sumBef;
}
void update (int idx, int sign) {
idx += numleaves;
numVals[idx] += sign;
sumVals[idx] += sign*(idx-numleaves);
idx /= 2;
while (idx > 0) {
numVals[idx] = numVals[2*idx] + numVals[2*idx+1];
sumVals[idx] = sumVals[2*idx] + sumVals[2*idx+1];
idx /= 2;
}
}
};
signed main() {
fastIO();
cin >> N >> K;
vals.resize(N);
Segtree sumQ(1020);
for (int i = 0; i < N; i++) {
cin >> vals[i].vote >> vals[i].colab;
sumQ.update(vals[i].vote, 1);
}
sort(vals.begin(), vals.end(), cmpVal);
// for (int i = 0; i < (int)vals.size(); i++) cerr << vals[i].colab << " ";
// cerr << "\n";
ld sumColab = 0;
ans = min(ans, (ld)sumQ.query(K));
for (int i = 0; i < K && vals[i].colab != -1; i++) {
sumColab += ((ld)vals[i].colab) / ((ld)(i + 1));
sumQ.update(vals[i].vote, -1);
ld sumVote = ((ld)sumQ.query(K-i-1)) / ((ld)(i + 2));
ans = min(ans, sumColab + sumVote);
}
cout << fixed << setprecision(12) << ans << "\n";
}
