#include <bits/stdc++.h>
using namespace std;
int i, n, m, x, y, ans, h[2200], l[2200];
int main() {
  scanf("%d%d", &n, &m);
  for (i = 1; i <= m; ++i) {
    scanf("%d%d", &x, &y);
    h[x] = l[y] = 1;
  }
  for (i = 2; i < n; ++i) {
    if (!h[i]) ans++;
    if (!l[i]) ans++;
  }
  if (n & 1 && !h[(n + 1) / 2] && !l[(n + 1) / 2]) ans--;
  printf("%d\n", ans);
}
