#include <bits/stdc++.h>
using namespace std;
int n, m;
int eatenr[1007];
int eatenc[1007];
int main() {
  scanf("%d%d", &n, &m);
  int i;
  int x, y;
  for (i = 0; i < m; i++) {
    scanf("%d%d", &x, &y);
    eatenr[x] = 1;
    eatenc[y] = 1;
  }
  if (n % 2 == 1) {
    if (eatenr[n / 2 + 1] == 0 && eatenc[n / 2 + 1] == 0) {
      eatenc[n / 2 + 1] = 1;
    }
  }
  int ans = 0;
  for (i = 2; i < n; i++) {
    if (eatenr[i] == 0) ans++;
    if (eatenc[i] == 0) ans++;
  }
  printf("%d\n", ans);
  return 0;
}
