#include <iostream>
#include <fstream>
#include <vector>
#include <algorithm>
#include <iomanip>
#define x first
#define y second
using namespace std;
using ld=long double;
ifstream fin("popandai.in");
ofstream fout("popandai.out");
const int Nmax=305;
pair<ld,ld> a[Nmax];
int cnt[Nmax][Nmax];
ld arie[Nmax][Nmax];
ld mina[Nmax];
struct triunghi
{
    int nr;
    ld A;
    bool operator < (triunghi cmp)
    {
        if(nr!=cmp.nr) return (nr<cmp.nr);
        return(A<cmp.A);
    }
};
vector<triunghi> up,down;
ld atrapez(pair<ld,ld> p1,pair<ld,ld> p2)
{
    if(p1.x>p2.x)
    {
        pair<ld,ld> aux;
        aux=p1;
        p1=p2;
        p2=aux;
    }
    return ((p2.x-p1.x)*(p1.y+p2.y)/2);
}
bool isright(pair<ld,ld> p1,pair<ld,ld> p2,pair<ld,ld> c)
{
    return ( (c.y-p1.y)*(p2.x-p1.x) - (c.x-p1.x)*(p2.y-p1.y) <=0 );
}
bool intrapez(pair<ld,ld> p1,pair<ld,ld> p2,pair<ld,ld> c)
{
    if(p1==p2)
    {
        if(c.x==p1.x && c.y<p1.y) return true;
        return false;
    }
    if(p1.x>p2.x)
    {
        pair<ld,ld> aux;
        aux=p1;
        p1=p2;
        p2=aux;
    }
    return(p1.x<=c.x && c.x<=p2.x && isright(p1,p2,c));
}
triunghi calct(int i,int j,int k)
{
    if(a[i].x>a[j].x)
    {
        int aux;
        aux=i;
        i=j;
        j=aux;
    }
    if(a[i].x>a[k].x)
    {
        int aux;
        aux=i;
        i=k;
        k=aux;
    }
    if(a[k].x>a[j].x)
    {
        int aux;
        aux=j;
        j=k;
        k=aux;
    }
    if(isright(a[i],a[j],a[k]))
    {
        triunghi t;
        t.nr=cnt[i][j]-cnt[i][k]-cnt[j][k]+cnt[k][k]-intrapez(a[i],a[j],a[k]);
        t.A=arie[i][j]-arie[i][k]-arie[j][k];
        return t;
    }
    else
    {
        triunghi t;
        t.nr=-cnt[i][j]+cnt[i][k]+cnt[j][k]-cnt[k][k];
        t.A=-arie[i][j]+arie[i][k]+arie[j][k];
        return t;
    }
}
void calc(int i,int j,int k)
{
    if(a[i].x>a[j].x)
    {
        int aux;
        aux=i;
        i=j;
        j=aux;
    }
    if(isright(a[i],a[j],a[k]))
    {
        triunghi t=calct(i,j,k);
        down.push_back(t);
    }
    else
    {
        triunghi t=calct(i,j,k);
        up.push_back(t);
    }
}
int main()
{
    int n,q;
    fin>>n>>q;
    for(int i=1; i<=n; i++)
    {
        fin>>a[i].x>>a[i].y;
    }
    for(int i=1; i<=n; i++)
    {
        for(int j=1; j<=n; j++)
        {
                arie[i][j]=atrapez(a[i],a[j]);
                for(int k=1; k<=n; k++)
                {
                    if(k!=i && k!=j)
                    {
                        cnt[i][j]+=intrapez(a[i],a[j],a[k]);
                    }
                }
        }
    }
    ld sol=-1;
    for(int i=1; i<=n; i++)
    {
        for(int j=i+1; j<=n; j++)
        {
            up.clear();
            down.clear();
            for(int k=1; k<=n; k++)
            {
                if(k!=i && k!=j)
                {
                    calc(i,j,k);
                }
            }
            if(up.size()!=0 && down.size()!=0)
            {
                sort(down.begin(),down.end());
                mina[down.size()-1]=down[down.size()-1].A;
                for(int k=down.size()-2; k>=0; k--)
                {
                    mina[k]=min(mina[k+1],down[k].A);
                }
                for(int k=0; k<up.size(); k++)
                {
                    int need=q-up[k].nr;
                    triunghi t;
                    t.nr=need;
                    t.A=-1;
                    int poz=lower_bound(down.begin(),down.end(),t)-down.begin();
                    if(poz!=down.size())
                    {
                        if(sol==-1) sol=up[k].A+mina[poz];
                        else sol=min(sol,up[k].A+mina[poz]);
                    }
                }
            }
        }
    }
    fout<<setprecision(1)<<fixed;
    fout<<sol<<'\n';
    return 0;
}