#pragma GCC optimize("Ofast")
#include<bits/stdc++.h>
using namespace std;
#define pb push_back
#define fi first
#define se second
#define sz(a) (int)(a.size())
#define all(a) a.begin(),a.end()
#define lb lower_bound
#define ub upper_bound
#define owo ios_base::sync_with_stdio(0);cin.tie(0);
#define debug(...) fprintf(stderr, __VA_ARGS__),fflush(stderr)
#define time__(d) for(long blockTime = 0; (blockTime == 0 ? (blockTime=clock()) != 0 : false);\
debug("%s time : %.4fs\n", d, (double)(clock() - blockTime) / CLOCKS_PER_SEC))
typedef long long int ll;
typedef long double ld;
typedef pair<ll,ll> PII;
typedef pair<int,int> pii;
typedef vector<vector<int>> vii;
typedef vector<vector<ll>> VII;
ll gcd(ll a,ll b){if(!b)return a;else return gcd(b,a%b);}
ll dp[555][555];
int main()
{
int n,K;
cin>>n>>K;
vector<pii>t(n);
vector<ll>a(n),b(n);
for(int i=0;i<n;i++){
cin>>t[i].fi>>t[i].se;
if(t[i].se == -1)t[i].se = 1e9;
swap(t[i].fi,t[i].se);
}
sort(all(t));
for(int i=0;i<n;i++){
a[i] = t[i].se;
b[i] = t[i].fi;
//cout<<a[i]<<" "<<b[i]<<'\n';
a[i] *= 1e9;
b[i] *= 1e9;
}
ll ans = 1e18;
for(int k=0;k<=K;k++){
//cout<<k<<'\n';
for(int i=0;i<n;i++){
for(int j=0;j<=n;j++)dp[i][j] = 1e18;
}
dp[0][1] = a[0]/(k+1);
if(b[0] != -1 && k)dp[0][0] = b[0];
else if(!k)dp[0][0] = 0;
for(int i=1;i<n;i++){
for(int j=0;j<=i+1;j++){
int c = i+1 - j;
if(b[i] != -1 && c<=k && c){ //add coord
dp[i][j] = min(dp[i][j],dp[i-1][j] + b[i]/c);
}
if(j){
dp[i][j] = min(dp[i][j],dp[i-1][j-1] + a[i]/(k+1));
}
if(c>k)dp[i][j] = min(dp[i][j],dp[i-1][j]);
// cout<<dp[i][j]/1e9<<" ";
}
// cout<<'\n';
}
for(int i=K-1;i<n;i++){
for(int j=0;j<=i+1;j++){
int c = min(k,i+1 - j);
if(c == k && c+j >= K)ans = min(ans,dp[i][j]);
}
}
}
ld fin = ans;
fin/=1e9;
cout<<fixed<<setprecision(5)<<fin<<'\n';
}
