#include <bits/stdc++.h>
#define int int64_t
using namespace std;
const int INF = 2e18;
signed main(){
ios_base::sync_with_stdio(false);
cin.tie(NULL);
//freopen("input.in", "r", stdin);
//freopen("output.out", "w", stdout);
int n, k; cin>>n>>k;
vector<array<int, 3>>bi(n);
vector<array<int, 3>>ai(n);
for(int i = 0; i<n; ++i){
int a, b; cin>>a>>b;
if(b == -1) b = INF;
ai[i] = {a, b, i};
bi[i] = {b, a, i};
}
sort(bi.begin(), bi.end());
sort(ai.begin(), ai.end());
vector<int>perm(n);
for(int i = 0; i<n; ++i){
perm[ai[i][2]] = i;
}
vector<long double>col_sum(n);
col_sum[0] = bi[0][0];
for(int i = 1; i<n; ++i){
col_sum[i] = col_sum[i-1] + ((long double)bi[i][0]/(i+1));
}
//for(auto u: col_sum) cout<<u<<" ";
//cout<<endl;
int sum = 0;
for(int i = 0; i<k; ++i) sum += ai[i][0];
vector<int>taken(n);
long double ans = sum;
int index = k-1;
for(int i = 0; i<k; ++i){
while(index >= 0 && taken[index]) --index;
if(perm[bi[i][2]] <= index){
taken[perm[bi[i][2]]] = 1;
sum -= bi[i][1];
}
else if(index != -1){
sum -= ai[index][0];
--index;
}
long double cur = col_sum[i] + ((long double)sum/(i+2));
ans = min(ans, cur);
}
cout<<setprecision(10)<<ans;
cout<<'\n';
}
