#include <bits/stdc++.h>
using namespace std;
#define PB push_back
#define ZERO (1e-10)
#define INF (1<<29)
#define CL(A,I) (memset(A,I,sizeof(A)))
#define DEB printf("DEB!"\n);
#define D(X) cout << "  "<<#X<<": "<<X<<endl;
#define EQ(A,B) (A+ZERO>B&&A-ZERO<B)
typedef long long ll;
typedef long long LINT;
typedef long double ld;
typedef pair<ll, ll> pll;
typedef vector<int> vi;
typedef pair<int, int> ii;
typedef vector<ii> vii;
#define IN(n) int n; scanf("%d", &(n));
#define FOR(i, m, n) for (int i(m); i<n; i++)
#define REP(i, n) FOR(i, 0, n)
#define F(n) REP(i, n)
#define FF(n) REP(j, n)
#define FT(m, n) FOR(k, m, n)
#define aa first
#define bb second
#define FI first
#define SE second
void ga(int N, int *A){F(N)scanf("%d",A+i);}
#define MX (1000009)
ii A[MX];
ll B,X;
int I,H,M,N,a,b,T;
multiset<int> S;
ll bst(){
    S.clear();
    if(N&1)return 2e18;
    sort(A,A+N),H=N/2,I=0,X=2e18,T=2e9;
    F(N){
        S.insert(-A[i].bb);
        while(i+1<N&&A[i].aa==A[i+1].aa)S.insert(-A[++i].bb);
        while(!S.empty()&&-*S.begin()>=T)S.erase(*S.begin());
        while(int(S.size())>H)T=min(T,-*S.begin()),S.erase(*S.begin());
        if((int)S.size()<H)continue;
        X=min(X,(A[i].aa+1)*1ll*-(*S.begin()-1));
    }
    return X;
}
void rt(int&a,int&b){
    int i=a,j=b;
    if(a<M/2&&b<M/2)a=i,b=M-j-1;
    else if(a<M/2&&b>=M/2)a=M-i-1,b=j;
    else if(a>=M/2&&b>=M/2)a=i,b=M-j-1;
    else if(a>=M/2&&b<M/2)a=M-i-1,b=j;
    else assert(0);
}
void rot(){
    F(N)rt(A[i].aa,A[i].bb);
}
int main(){
    while(~scanf("%d%d",&M,&N)){
        B=2e18;
        F(N)scanf("%d%d",&a,&b),A[i]={a,b};
        F(4){
            B=min(B,bst());
            rot();
            F(N)swap(A[i].aa,A[i].bb);
            B=min(B,bst());
            F(N)swap(A[i].aa,A[i].bb);
        }
        if(B>1e18)puts("-1");
        else printf("%lld\n",B);
    }
    return 0;
}