#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define ld long double
const bool Multitest = 0;
const int N = 505; const ll offset = 1e9;
int n, k;
struct Type
{
ld x, y;
}; Type a[N];
bool cmp1(Type a, Type b)
{
return a.y < b.y || (a.y == b.y && a.x < b.x);
}
namespace sub345
{
const int M = 105;
ld dp[M][M][M];
void minimize(ld& a, ld b)
{
a = min(a, b);
}
void solve()
{
for(int i = 0 ; i <= n ; i++)
{
for(int j = 0 ; j <= i ; j++)
{
for(int k = 1 ; k <= j + 1 ; k++)
{
dp[i][j][k] = 1e18;
}
}
}
sort(a + 1, a + 1 + n, cmp1);
dp[0][0][1] = 0;
for(int i = 0 ; i < n ; i++)
{
for(int j = 0 ; j <= i && j <= k; j++)
{
for(int cnt = 1 ; cnt <= j + 1 ; cnt++)
{
minimize(dp[i + 1][j + 1][cnt], dp[i][j][cnt] + (a[i + 1].x / cnt));
minimize(dp[i + 1][j + 1][cnt + 1], dp[i][j][cnt] + (a[i + 1].y / cnt));
minimize(dp[i + 1][j][cnt], dp[i][j][cnt]);
// cout << i << ' ' << j << ' ' << cnt << ' ' << dp[i][j][cnt] << " ---> " << dp[i + 1][j][cnt] << '\n';
}
}
// cout << dp[i][4][1] << '\n';
}
ld ans = 1e18;
// cout << dp[4][4][1 ] << '\n'/
for(int x = 1 ; x <= k + 1 ; x++) minimize(ans, dp[n][k][x]);
cout << setprecision(9) << fixed << ans ;
}
}
void work()
{
cin >> n >> k;
for(int i = 1 ; i <= n ; i++)
{
cin >> a[i].x >> a[i].y;
if(a[i].y == -1) a[i].y = 1e9;
}
if(n <= 100) sub345::solve();
}
int main()
{
ios_base::sync_with_stdio(false);
cin.tie(0); cout.tie(0);
int q = 1;
if(Multitest) cin >> q;
while(q--) work();
}
