#include <bits/stdc++.h>
using namespace std;
void setup()
{
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
}
struct FENWICK_TREE
{
int num[501], tree[501];
inline void Update(int x, int v, int o)
{
while (x <= 500)
{
tree[x] += v * o;
num[x] += o;
x += (x & (~(x - 1)));
}
}
inline int Get(int v)
{
int res = 0, x = 0;
for (int i = 10; i >= 0; --i)
{
if (x + (1 << i) <= 500 && num[x + (1 << i)] <= v)
{
x += (1 << i);
res += tree[x];
v -= num[x];
}
}
return res;
}
} ft;
int n, m;
double res = 0, sum;
array<int, 3> p[500];
int main()
{
setup();
cin >> n >> m;
for (int i = 0; i < n; ++i)
{
cin >> p[i][0] >> p[i][1];
p[i][1] = (p[i][1] == -1 ? 2000 : p[i][1]);
}
sort(p, p + n);
for (int i = 0; i < n; ++i)
{
res += p[i][0] * (i < m);
p[i][2] = i + 1;
ft.Update(p[i][2], p[i][0], 1);
swap(p[i][0], p[i][1]);
}
sort(p, p + n);
for (int i = 0; i < m; ++i)
{
if (p[i][0] == 2000)
{
break;
}
sum += (double)p[i][0] / (i + 1);
ft.Update(p[i][2], p[i][1], -1);
res = min(res, sum + (double)ft.Get(m - i - 1) / (i + 2));
}
cout << fixed << setprecision(6) << res;
return 0;
}
