#include <bits/stdc++.h>
int main() {
  int n, m;
  int sum = 0;
  int a, b;
  int i = 0;
  int x[1010] = {0}, y[1010] = {0};
  scanf("%d %d", &n, &m);
  while (m-- > 0) {
    scanf("%d %d", &a, &b);
    y[a] = 1;
    x[b] = 1;
  }
  for (i = 2; i <= n - 1; i++) {
    if (x[i] == 0) sum++;
    if (y[i] == 0) sum++;
  }
  if (n % 2 == 1 && x[n / 2 + 1] == 0 && y[n / 2 + 1] == 0) sum--;
  printf("%d\n", sum);
  return 0;
}
