#include <bits/stdc++.h>
using namespace std;
char A[1005][1005];
int RF[1005], CF[1005], N, M;
int i, j, x, y, k, sol, m4;
int main() {
  scanf("%d%d", &N, &M);
  for (i = 2; i < N; i++) RF[i] = CF[i] = 1;
  for (i = 1; i <= M; i++) {
    scanf("%d%d", &x, &y);
    RF[x] = 0;
    CF[y] = 0;
  }
  for (i = 1; i <= N / 2; i++) {
    m4 = RF[i] + RF[N - i + 1] + CF[i] + CF[N - i + 1];
    sol += m4;
  }
  if (N % 2 == 1) {
    sol += max(RF[(N + 1) / 2], CF[(N + 1) / 2]);
  }
  printf("%d\n", sol);
  return 0;
}
