#include <bits/stdc++.h>
#define int long long
using namespace std;
const long long N = 2e5 + 5;
void solve()
{
int n, k;
cin >> n >> k;
vector<pair<int, int>> a(n);
for (int i = 0; i < n; i++)
{
cin >> a[i].first >> a[i].second;
if (a[i].second == -1)
{
a[i].second = 1e18;
}
}
sort(a.begin(), a.end());
// , [&](pair<int, int> a, pair<int, int> b)
// {if (a.second==b.second)
// return a.first < b.first;
// return a.second < b.second; });
double answer;
int people = 1;
for (int i = 0; i < k; i++)
{
answer += a[i].first / people;
if (a[i].second != 1e18)
people++;
}
cout << answer;
}
signed main()
{
cout << fixed << setprecision(10);
ios_base::sync_with_stdio(0);
cin.tie(NULL);
cout.tie(NULL);
int t = 1;
// cin >> t;
for (int i = 1; i <= t; i++)
{
// cout << "Case #" << i << ':' << ' ';
solve();
cout << endl;
}
return 0;
}
