#include <iostream>
#include <iomanip>
#include <vector>
#include <cmath>
#include <algorithm>
#include <set>
#include <queue>
#include <map>
#include <stack>
#include <bitset>
#include <string>
#include <cstring>
#include <iterator>
#include <random>
using namespace std;
typedef long long ll;
typedef pair<ll, ll> pll;
typedef long double ld;
const ll dim = 3*1e3+7;
//const ll mod = 1e9 + 7;
const ld inf = 1e17+7;
#define endl "\n"
#define fi first
#define pb push_back
#define se second
#define vll vector<ll>
ll n, m;
pll a[dim];
ld dp[600][600];
int main() {
ll t, u0, v0;
cin>>n>>m;
for(int i=1; i<=n; i++){
cin>>a[i].se>>a[i].fi;// se- a fi-b
if(a[i].fi==-1)a[i].fi=inf;
}
for(int i=0; i<=n; i++){
for(int j=1; j<=n; j++){
dp[i][j]=(ld)inf;
}
}
for(int i=0; i<=n; i++){
dp[i][0]=(ld)0;
}
sort(a+1, a+1+n);
multiset<ll> op;
ld ans=(ld)inf;
for(int i=1; i<=n; i++){
ll sum=0;
op.clear();
for(int j=i+1; j<=n; j++){
op.insert(a[j].se);
}
for(int j=i+1; j<=m; j++){
sum+=(*op.begin());
op.erase(op.begin());
}
for(int k=m; k>=0; k--){
for(int j=k; j>=1; j--){
ld op1=+(ld)a[i].se/ (ld)(k+1);
ld op2=+(ld)a[i].fi/ (ld)j;
dp[k][j]=min<ld>(dp[k][j]+op1, dp[k][j-1]+op2);
}
dp[k][0]=dp[k][0]+(ld)(a[i].se)/(ld)(k+1);
if(k==0){
// cout<<dp[0][0]<<endl;
}
ans=min<ld>(ans, dp[k][k] +(ld)sum/(k+1));
}
}
cout<<fixed<<setprecision(10)<<ans<<endl;
return 0;
}
