#pragma comment(linker, "/STACK:60777216")  

#include <cassert>
#include<iostream>
#include<algorithm>
#include<cstdio>
#include<complex>
#include<vector>
#include<cstring>
#include<set>
#include<map>
#include<cmath>
#include<queue>
#include<string>
#include<cstdlib>
#include<memory.h>
#include<ctime>
#include<bitset>
#include<fstream>
#include<queue>
#include<stack>
#include<unordered_map>
#include<unordered_set>

using namespace std;

typedef long double ld;

typedef long long ll;
typedef pair<int,int>	pii;
typedef pair<ld,ld>	pdd;
typedef vector<int> vi;
typedef vector<ld> vd;
typedef pair<ll,ll> pl;

#define FOR(i,a,b)		for(int i=(a);i<(b);i++)	
#define REP(i,n)		FOR(i,0,n)
#define SORT(v)			sort((v).begin(),(v).end())
#define UN(v)			SORT(v),(v).erase(unique((v).begin(),(v).end()),(v).end())
#define CL(a,b)			memset(a,b,sizeof a)
#define pb				push_back

int n,k;
int x[55],y[55];

ll r[51][51][51][51][2];

ll sq(ll x1,ll x2,ll x3){
	return (x[x2]-x[x1])*ll(y[x3]-y[x1])-(x[x3]-x[x1])*ll(y[x2]-y[x1]);
}

ll go(int prev,int prevprev,int to,int num,int type){
	ll& d = r[prev][prevprev][to][num][type];
	if(d!=-1) return d;
	d=-2;
	if(num==0){
		if(prevprev==to) return d=(y[prev]+y[to])*ll(x[to]-x[prev]);
		if(x[prev]>=x[to]) return d=-2;
		if(sq(prevprev,prev,to)*(type==0?1:-1)<0) return d=(y[prev]+y[to])*ll(x[to]-x[prev]);
		return d=-2;
	}else{
		REP(i,n)if(x[i]>x[prev] && x[i]<x[to]){
			if(sq(prevprev,prev,i)*(type==0?1:-1)>=0) continue;
			ll v = go(i,prev,to,num-1,type);
			if(v==-2)continue;
			v += (y[prev] + y[i])*ll(x[i]-x[prev]);
			if(d==-2 || d<v)d=v;
		}
	}
	return d;
}

ll solve(int from,int to,int num,int type){
	return go(from,to,to,num,type);
}

int main(){	
#ifdef LocalHost
	freopen("input.txt","r",stdin);
	//freopen("output.txt","w",stdout);
#endif
#ifndef LocalHost
	freopen("farm.in","r",stdin);
	freopen("farm.out","w",stdout);
#endif

	CL(r,-1);

	cin>>n>>k;
	REP(i,n)scanf("%d %d",x+i,y+i);

	
	if(k<=2) {puts("-1");return 0;}
	ll res = -1;
	REP(i,n)REP(j,n)if(x[i]<x[j]){
		REP(t1,k-2+1){
			ll s1 = solve(i,j,t1,0);
			ll s2 = solve(i,j,k-2-t1,1);
			if(s1!=-2 && s2!=-2){
				if(res==-1 || res<s1-s2)res=s1-s2;
			}
		}
	}
	REP(i,n)REP(j,n)REP(i1,n)if(x[i]<x[j] && x[i1]==x[i] && y[i1]<y[i]){
		REP(t1,k-3+1){
			ll s1 = solve(i,j,t1,0);
			ll s2 = solve(i1,j,k-3-t1,1);
			if(s1!=-2 && s2!=-2){
				if(res==-1 || res<s1-s2)res=s1-s2;
			}
		}
	}
	REP(i,n)REP(j,n)REP(i1,n)if(x[i]<x[j] && x[i1]==x[j] && y[i1]<y[j]){
		REP(t1,k-3+1){
			ll s1 = solve(i,j,t1,0);
			ll s2 = solve(i,i1,k-3-t1,1);
			if(s1!=-2 && s2!=-2){
				if(res==-1 || res<s1-s2)res=s1-s2;
			}
		}
	}
	REP(i,n)REP(i1,n)if(x[i]==x[i1] && y[i]>y[i1])REP(j,n)REP(j1,n)if(x[j]==x[j1] && y[j1]<y[j])if(x[i]<x[j]){
		REP(t1,k-4+1){
			ll s1 = solve(i,j,t1,0);
			ll s2 = solve(i1,j1,k-4-t1,1);
			if(s1!=-2 && s2!=-2){
				if(res==-1 || res<s1-s2)res=s1-s2;
			}
		}
	}
	cout<<res<<endl;
#ifdef LocalHost
	printf("TIME: %.3lf\n",ld(clock())/CLOCKS_PER_SEC);
#endif
	return 0;
}