#include <bits/stdc++.h>
#define REP(A,B) for(int (A)=0;(A)<(B);(A)++)
#define ll long long
#define X first
#define Y second
#define pii pair<ll, ll>
#define mp make_pair
#define pb push_back
using namespace std;
int n,m;
ll solve(vector<pii>& PTS) {
	priority_queue< pair<int, int>, vector<pii>, less<pii> > Q;
	ll ans = 1LL<<62;
	int i;
	ll lastpop = 1LL<<62;
	int lastYYY = 0;
	for(i=0;i < n; ) {
		int lastj = i;
		for(int j = i; j < n && PTS[j].Y==PTS[i].Y; j++) {
			Q.push(PTS[j]);
	//		printf("adding %lld %lld to the heap.\n", PTS[j].X, PTS[j].Y);
			lastYYY = PTS[j].Y;
			lastj = j;
		}
		i = lastj+1;
		if(2*Q.size() >= n)
			break;
	}
	while(i < n) {
		while(2*Q.size() > n) {
			pii it = Q.top();
			lastpop = min(it.X, lastpop);
			Q.pop();
			ll x1 = it.X;
			while(!Q.empty()) {
				auto curr = Q.top();
				if(curr.X != x1)
					break;
				Q.pop();
			}
		}
		if(2*Q.size() == n) {
			pii topright = Q.top();
			//printf("lastYYY=%lld, tR=%lld\n", lastYYY, topright.X);
			ans = min(ans, (lastYYY+1)*(topright.X+1));
		}
		do {
			ll yy1 = PTS[i].Y;
			
			for(; i < n; i++) {
				if(PTS[i].Y != yy1)
					break;
				if(PTS[i].X < lastpop) {
					Q.push(PTS[i]);
		//			printf("adding %lld %lld to the heap.\n", PTS[i].X, PTS[i].Y);
					lastYYY = PTS[i].Y;
				}
			}
		} while(i < n && 2*Q.size() < n);
	}
		while(2*Q.size() > n) {
			pii it = Q.top();
			lastpop = min(it.X, lastpop);
			Q.pop();
			ll x1 = it.X;
			while(!Q.empty()) {
				auto curr = Q.top();
				if(curr.X != x1)
					break;
				Q.pop();
			}
		}
		if(2*Q.size() == n) {
			pii topright = Q.top();
			//printf("lastYYY=%lld, tR=%lld\n", lastYYY, topright.X);
			ans = min(ans, (lastYYY+1)*(topright.X+1));
		}
	return ans;

}

int main() {
	while(scanf("%d%d", &m, &n)==2) {
		vector<pii> PTS;
		REP(i, n) {
			ll xxx, yyy;
			scanf("%lld%lld", &xxx, &yyy);
			PTS.pb(mp(xxx, yyy));
		}
		vector<pii> PTS2=PTS;
		sort(PTS.begin(), PTS.end(), [](pii a, pii b){
			return a.Y<b.Y;
		});
		ll ans = solve(PTS);
		REP(i, n) {
			PTS[i] = mp(m-PTS2[i].X-1, PTS2[i].Y);
		}
		sort(PTS.begin(), PTS.end(), [](pii a, pii b){
			return a.Y<b.Y;
		});
		ans = min(solve(PTS), ans);
		REP(i, n) {
			PTS[i] = mp(m-PTS2[i].X-1, m-PTS2[i].Y-1);
		}
		sort(PTS.begin(), PTS.end(), [](pii a, pii b){
			return a.Y<b.Y;
		});
		ans = min(solve(PTS), ans);
		REP(i, n) {
			PTS[i] = mp(PTS2[i].X, m-PTS2[i].Y-1);
		}
		sort(PTS.begin(), PTS.end(), [](pii a, pii b){
			return a.Y<b.Y;
		});
		ans = min(solve(PTS), ans);
		if(ans == 1LL<<62)
			ans = -1;
		printf("%lld\n", ans);
	}
	return 0;
}