#include <bits/stdc++.h>
using namespace std;
bool xfla[1005], yfla[1005];
int n, m, x, y, tmp;
int main() {
  scanf("%d%d", &n, &m);
  memset(xfla, 0, sizeof(xfla));
  memset(yfla, 0, sizeof(yfla));
  for (int i = 0; i < m; i++) {
    scanf("%d%d", &x, &y);
    xfla[x] = 1;
    yfla[y] = 1;
  }
  int ans = 0;
  for (int i = 2; i < n; i++) {
    if (!xfla[i]) ans++;
    if (!yfla[i]) ans++;
  }
  if (n % 2 == 1) {
    tmp = n / 2 + 1;
    if (!xfla[tmp] && !yfla[tmp]) ans--;
  }
  printf("%d\n", ans);
  return 0;
}
