#include <bits/stdc++.h>

using namespace std;

typedef long long int ll;
typedef long double ld;

typedef pair<ll, ll> ii;
typedef vector<ll> vi;
typedef vector<ii> vii;

#define PB push_back

#define FOR(prom,a,b) for( ll prom = (a); prom < (ll)(b); ++prom )
#define F(a) FOR(i,0,a)
#define FF(a) FOR(j,0,a)

#define EPS (1e-10)
#define INF ((1LL<<62LL)-1LL)

#define EQ(a,b) (fabs(a-b)/fabs(a+b) < EPS)
ll M,N;
ll solve(vii &a){
	set<ii> s;
	ll r=INF,right=M;
	F(a.size()){
			ll j=a[i].first;
			if(a[i].second > right)continue;
			s.insert({a[i].second,a[i].first});
			if(i!=a.size()-1 && a[i].first==a[i+1].first)continue;
			while(s.size()>N/2){
					auto it=s.end();--it;
					right=it->first-1;
					while(s.size()>0 && it->first > right){
						s.erase(it);
						if(s.size()==0)break;
						it=s.end();--it;
					}
			}
//			for ( auto x : s ) {
//				cerr << "[" << x.first <<' '<<x.second<<"] ";
//			} cerr << endl;
			if(s.size()==N/2){
//					cout<<" t:"<<s.rbegin()->second<<' '<<j<<endl;
//					if(s.rbegin()->second!=j)continue;
//					cout<<" set:"<<((i+1) * (s.rbegin()->first+1))<<endl;
					r=min(r,(j+1) * (s.rbegin()->first+1));
//					cout<<r<<endl;
			}
	}
	return r;
}

int main ()
{
	ios::sync_with_stdio(false);
	while(cin>>M>>N){
			vii a[4];
			F(N){
					ll x,y;cin>>x>>y;
					a[0].PB({y,x});
					a[1].PB({M-1-y,x});
					a[2].PB({y,M-1-x});
					a[3].PB({M-1-y,M-1-x});
			}
			F(4)sort(a[i].begin(),a[i].end());
			if(N%2){
					cout<<-1<<endl;
					continue;
			}
			ll r=INF;
			F(4){
					r=min(r,solve(a[i]));
			}
			cout<<(r==INF?-1:r)<<endl;
	}

	return 0;
}