#include <bits/stdc++.h>
#define ll long long
#define INF 1000000005
#define MOD 1000000007
#define EPS 1e-10
#define rep(i,n) for(int i=0;i<(int)(n);++i)
#define rrep(i,n) for(int i=(int)(n)-1;i>=0;--i)
#define srep(i,s,t) for(int i=(int)(s);i<(int)(t);++i)
#define each(a,b) for(auto& (a): (b))
#define all(v) (v).begin(),(v).end()
#define len(v) (int)(v).size()
#define zip(v) sort(all(v)),v.erase(unique(all(v)),v.end())
#define cmx(x,y) x=max(x,y)
#define cmn(x,y) x=min(x,y)
#define fi first
#define se second
#define pb push_back
#define show(x) cout<<#x<<" = "<<(x)<<endl
#define spair(p) cout<<#p<<": "<<p.fi<<" "<<p.se<<endl
#define sar(a,n) cout<<#a<<":";rep(pachico,n)cout<<" "<<a[pachico];cout<<endl
#define svec(v) cout<<#v<<":";rep(pachico,v.size())cout<<" "<<v[pachico];cout<<endl
#define svecp(v) cout<<#v<<":";each(pachico,v)cout<<" {"<<pachico.first<<":"<<pachico.second<<"}";cout<<endl
#define sset(s) cout<<#s<<":";each(pachico,s)cout<<" "<<pachico;cout<<endl
#define smap(m) cout<<#m<<":";each(pachico,m)cout<<" {"<<pachico.first<<":"<<pachico.second<<"}";cout<<endl
 
using namespace std;
 
typedef pair<int,int> P;
typedef pair<ll,ll> pll;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<ll> vl;
typedef vector<vl> vvl;
typedef vector<double> vd;
typedef vector<P> vp;
typedef vector<string> vs;
 
const int MAX_N = 100005;
const double s3 = sqrt(3.0);
 
inline double rpos(P& p, int y){
    return (s3*p.fi+p.se-y)*s3/3.0;
}
 
inline double lpos(P& p, int y){
    return (s3*p.fi-p.se+y)*s3/3.0;
}
 
#define getchar getchar_unlocked
 
inline int in() {
    int n = 0; short c; bool flag = false;
    if((c = getchar()) < '0') flag = true; else n = c - '0';
    while ((c = getchar()) >= '0') n = n * 10 + c - '0';
    return flag ? -n : n;
}
 
int main()
{
    while(1){
        int n = in();
        if(n == 0) break;
        int K = in();
        map<int,int> mp;
        vp l(n),r(n);
        rep(i,n){
            int a = in(), b = in();
            mp[b]++;
            l[i] = P(a,b), r[i] = P(a,b);
        }
        sort(all(l),[&](P& a, P& b){
            return a.se-s3*a.fi < b.se-s3*b.fi;
        });
        sort(all(r),[&](P& a, P& b){
            return a.se+s3*a.fi < b.se+s3*b.fi;
        });
        double ans = 1e100;
        int cnt = 0;
        each(it,mp){
            if(cnt > K) break;
            int lid, rid;
            int made = 0;
            for(rid = 0; rid < n; rid++){
                if(r[rid].se + EPS >= it.fi){
                    if(++made == n-K) break;
                }
            }
            for(lid = n-1; lid >= 0; lid--){
                if(l[lid].se + EPS >= it.fi && l[lid].se <= -s3*l[lid].fi + r[rid].se + s3*r[rid].fi + EPS) break;
            }
            cmn(ans, rpos(r[rid],it.fi)-lpos(l[lid],it.fi));
            rep(i,K-cnt){
                bool ok = false;
                rid++;
                for(; rid < n; rid++){
                    if(r[rid].se + EPS >= it.fi && r[rid].se <= s3*r[rid].fi + l[lid].se - s3*l[lid].fi + EPS){
                        ok = true;
                        break;
                    }
                }
                if(!ok) break;
                ok = false;
                lid--;
                for(; lid >= 1; lid--){
                    if(l[lid].se + EPS >= it.fi && l[lid].se <= -s3*l[lid].fi + r[rid].se + s3*r[rid].fi + EPS){
                        ok = true;
                        break;
                    }
                }
                if(!ok) break;
                cmn(ans, rpos(r[rid],it.fi)-lpos(l[lid],it.fi));
            }
            cnt += it.se;
        }
        printf("%.12lf\n", 3.0*ans);
    }
    return 0;
}


Measured memory_bytes: 3676