#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#define pb push_back
#define int long long
#define repp(i,x,n) for(int i=x;i<=n;i++)
#define rep(i,x,n) for(int i=x;i>=n;i--)
#define r0 return 0
#define fi first
#define se second
#define liow ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL)
#define jelek cout<<"jelek"<<endl
#define pii pair<int,int>
#define all(v) v.begin(),v.end()
#define tp tuple<int,int,int>
#define fl fflush(stdout)
#define ld long double
#define p5 pair<int,pair<pair<int,int>,pair<int,int>>>
#pragma GCC optimize ("O2")
#pragma GCC optimize ("unroll-loops")
using namespace std;
using namespace __gnu_pbds;
typedef tree<int,null_type,less<int>,rb_tree_tag,tree_order_statistics_node_update> ordered_set;
typedef tree<pair<int,int>, null_type, less<pair<int,int>>, rb_tree_tag, tree_order_statistics_node_update> ordered_multiset;
//const int mod=1e9+7;
const int SQMAX=635,INF=1e18;
const int mod=998244353;
//const int MOD=1e6+3;
mt19937_64 rng((unsigned int) chrono::steady_clock::now().time_since_epoch().count());
pii dr[8]={{-1,0},{-1,1},{0,1},{1,1},{1,0},{1,-1},{0,-1},{-1,-1}};
int dx[4]={1,0,-1,0};
int dy[4]={0,1,0,-1};
int dxx[4]={1,1,-1,-1};
int dyy[4]={1,-1,-1,1};
int mul(int x,int y){return (x%mod*y%mod)%mod;}
int expo(int b,int e){
if(e==0) return 1;
int tmp=expo(b,e/2);
if(e%2) return mul(tmp,mul(tmp,b));
else return mul(tmp,tmp);
}
const int maxn=1e6;
bool cmp(pii x,pii y){
if(x.se!=y.se) return x.se<y.se;
return x.fi<y.fi;
}
void solve(){
int n,k;cin>>n>>k;
pii a[n+2];
repp(i,1,n){
cin>>a[i].fi>>a[i].se;
if(a[i].se==-1) a[i].se=INF;
}
sort(a+1,a+n+1,cmp);
ld suf[n+2][k+2];
repp(j,0,k+1) suf[n+1][j]=INF;
suf[n+1][0]=0;
for(int i=n;i>=1;i--){
for(int j=0;j<=k;j++){
//ambil
suf[i][j]=INF;
if(j>0){
suf[i][j]=min(suf[i][j],suf[i+1][j-1]+a[i].fi);
}
//ga
suf[i][j]=min(suf[i][j],suf[i+1][j]);
}
}
ld dp[k+2][k+2];
ld ans=INF;
repp(buff,0,k){
dp[0][0]=0;
if(buff==0){
ans=min(ans,suf[1][k]/(ld)(buff+1));
}
repp(i,1,buff) dp[0][i]=INF;
for(int i=1;i<=k;i++){
for(int j=0;j<=buff;j++){
dp[i][j]=INF;
//ambil buff
if(j>0 && a[i].se!=INF){
dp[i][j]=min(dp[i][j],dp[i-1][j-1]+(ld)a[i].se/(ld)(j));
}
//ga
dp[i][j]=min(dp[i][j],dp[i-1][j]+(ld)(a[i].fi)/(ld)(buff+1));
if(j==buff){
ans=min(ans,dp[i][j]+suf[i+1][k-i]/(ld)(buff+1));
}
}
}
}
cout<<fixed<<setprecision(10)<<ans<<endl;
}
signed main(){
liow;
int t=1;
// cin>>t;
while(t--){
solve();
}
}
