#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#define fst first
#define snd second
#define pb push_back
#define forn(i,a,b) for(int i = a; i < b; i++)
#define ALL(x) x.begin(),x.end()
#define SZ(x) (int)x.size()
#define mset(a,v) memset((a),(v),sizeof(a))
#define FIN ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
#define dbg(v) cout<<"Line("<<__LINE__<<"): "<<#v<<" = "<<v<<'\n';
#define pi pair<int,int>
#define pll pair<ll,ll>
typedef long long ll;
using namespace std;
using namespace __gnu_pbds;
typedef tree<int,null_type,less<int>,rb_tree_tag,tree_order_statistics_node_update> indexed_set;
typedef tree<int,null_type,less_equal<int>,rb_tree_tag,tree_order_statistics_node_update> indexed_multiset;
const int MAXN = 501;
long double dp[MAXN][MAXN][MAXN];
bool vis[MAXN][MAXN][MAXN];
ll n,k;
vector<pair<long double,long double>> s;
long double f(ll x, ll y, long double z){
//cout<<x<<" "<<y<<" "<<z<<'\n';
long double &res = dp[x][y][(ll)z];
//cout<<res<<" "<<vis[x][y][(ll)z]<<'\n';
if(vis[x][y][(ll)z]) return res;
if(y==k) return (long double)0;
if(x==n) return (long double)10000000000000000;
vis[x][y][(ll)z]=true;
//cout<<x<<" "<<y<<" "<<z<<'\n';
res=0;
res=f(x+1,y,z);
res=min(res,f(x+1,y+1,z)+s[x].snd/z);
if(s[x].fst>0)res=min(res,f(x+1,y+1,z+1)+s[x].fst/z);
//cout<<x<<" "<<y<<" "<<z<<" ->>>> "<<res<<'\n';
return res;
}
int main(){FIN;
cin>>n>>k;
s.clear();
s.resize(n);
forn(i,0,n){ cin>>s[i].snd>>s[i].fst; if(s[i].fst==-1){ s[i].fst=(long double)10000000000000000; }}
sort(ALL(s));
forn(i,0,MAXN) forn(j,0,MAXN) forn(h,0,MAXN) vis[i][j][h]=false;
//cout<<"llego\n";
cout<<fixed<<setprecision(15)<<f(0,0,1)<<'\n';
return 0;
}
