#include <bits/stdc++.h>

using namespace std;

#define rep(i, a, n) for (int i=(a); i < (n); i++)
#define per(i, a, n) for (int i=(n)-1; i >= (a); i--)
#define ll long long
#define x first
#define y second
const ll INF = 2e18;
typedef pair<ll,ll> pt;

int n;

	ll m;
	
ll go(vector<pair<pt,int>> &xo){
	ll res = INF;
	sort(xo.begin(), xo.end());
	set<pt> active;
	set<pt> xs;
	//for(auto a : xo) cout << a.x.x << " " << a.x.y << endl;
	//cout<<"---------"<<endl;
	ll minY = -1;
	rep(i,0,n){
		if(xo[i].x.y > minY) {
			active.insert({xo[i].x.y, xo[i].x.x});
			xs.insert({xo[i].x.x, xo[i].x.y});
		}
		if(i < n-1 && xo[i+1].x.x == xo[i].x.x){
			continue;
		}
		//cout << xo[i].y << ": "<<yo[yi].x.y << ": ";
		//for(auto asdf : active) cout << asdf<<" ";cout<<endl;
		while(active.size() > (n / 2)){
			ll tr =active.begin()->first;
			//cout<<xo[i].x.x<<"/"<<xo[i].x.y<<" "<<xo[i].y<<": "<<minY<<" "<<tr<<endl;
			assert(minY < tr); 
			minY = tr;
			while(true) {
				auto a = active.begin();
				if(active.size() && (a->first) == minY){} else break;
				xs.erase({a->second, a->first});
				active.erase(active.begin());
			}
		}
		if(active.size() == n/2){
			//for(auto a : xs) cout << a << " "; cout << endl;
			ll cur = (((--xs.end())->first) + 1) * (m - active.begin()->first);
			//ll cur = (xo[i].x.x+1) * (m-yo[yi].x.y);
			//cout << "yes " << (xo[i].x.x + 1) <<" " << (m - active.begin()->first) << ": " << cur << endl;
			res = min(res, cur);
		}
	}
	return res;
}

int main(void) {

	while(cin>>m>>n){
		vector<pair<pt,int>> v(n);
		rep(i,0,n)cin>>v[i].x.x>>v[i].x.y;
		//cout<<n<< " "<<m<<"!!"<<endl;
		if(n%2) {
			cout<<-1<<endl;
			continue;
		}
		ll res = INF;
		rep(i,0,4){
			res = min(res, go(v));
			rep(j,0,n) {
				swap(v[j].x.x, v[j].x.y);
				v[j].x.y = m - 1 - v[j].x.y;
			}
		}
		if(res == INF) res = -1;
		cout << res << endl;
	}
	return 0;
}