#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
#define MAXN (300005)
int main() {
ios_base::sync_with_stdio(false);cin.tie(0);
ll N,K;
cin>>N>>K;
deque<pair<ll,ll> > arr;
for(ll i = 1;i <= N;i++){
ll a,b;
cin>>a>>b;
if(b == -1) b = 1e18;
arr.push_back(make_pair(b,a));
}
sort(arr.begin(),arr.end());
arr.push_front(make_pair(0,0));
ld A[N + 1], B[N + 1]; //1-indexed
A[0] = 0;
B[0] = 0;
for(ll i = 1;i <= N;i++){
A[i] = arr[i].second;
B[i] = arr[i].first;
}
ld dp[N + 5][N + 5]; //first i states considered, j of them belong in B[i] = -1
ld ans = 1e18;
for(ll m = 0;m <= K;m++){ //m collaborators gained in total
for(ll i = 0;i <= N;i++){
for(ll j = 0;j <= N;j++){
dp[i][j] = 1e18;
}
}
dp[0][0] = 0;
for(ll i = 1;i <= N;i++){ //first i states considered
for(ll j = 0;j <= i;j++){ //j states are non-collaborators
ld valA = A[i] / (m + 1);
ld valB = B[i] / min(i - j,m);
dp[i][j] = min(dp[i][j],dp[i - 1][j] + valB);
if(i - j > m) dp[i][j] = min(dp[i][j],dp[i - 1][j]);
if(j >= 1) dp[i][j] = min(dp[i][j],dp[i - 1][j - 1] + valA);
}
}
ans = min(ans,dp[N][K - m]);
}
cout<<fixed<<setprecision(10);
cout<<ans<<'\n';
}
