#include<bits/stdc++.h>
#define lb long double
using namespace std;
const int maxn=502;
const int inf=1e8;
lb dp[2][maxn][maxn]; // dp[i][j][k]=min de tempo, para ter j votos e k colaboradores, com os i primeiros caras
pair<lb,lb> v[maxn];
bool cmp(pair<lb,lb> a, pair<lb,lb> b){
if(a.second!=b.second){
if(a.second==-1) return false;
if(b.second==-1) return true;
return a.second<b.second;
}
return a.first<b.first;
}
int main(){
ios_base::sync_with_stdio(false); cin.tie(nullptr); cout.tie(nullptr);
int n, m; cin >> n >> m;
for(int i=1;i<=n;i++) cin>> v[i].first >> v[i].second;
sort(v+1,v+1+n,cmp);
for(int i=0;i<=1;i++){
for(int j=0;j<=n;j++)
for(int k=0;k<=n+1;k++) dp[i][j][k]=inf;
dp[i][0][1]=0;
}
dp[1][0][1]=0; dp[1][1][1]=v[1].first;
if(v[1].second!=-1) dp[1][1][2]=v[1].second;
lb resp=inf;
if(m==1) resp=v[1].first;
for(int i=2;i<=n;i++){
//cout << i << ": " << endl;
int par=i%2, inv=1^par;
for(int j=1;j<=i;j++){
for(int k=1;k<=j+1;k++){
dp[par][j][k]=min(dp[inv][j][k],dp[par][j][k]);
if(k!=j+1) dp[par][j][k]=min(dp[inv][j-1][k]+(v[i].first/k),dp[par][j][k]);
if(k!=1&&v[i].second!=-1) dp[par][j][k]=min(dp[inv][j-1][k-1]+(v[i].second/(k-1)),dp[par][j][k]);
if(j>=m) resp=min(resp,dp[par][j][k]);
//cout << dp[i][j][k] << " ";
}
//cout << endl;
}
//cout << endl;
}
cout << fixed << setprecision(16) << resp << endl;
}
