#include <bits/stdc++.h>
const int MAXN = 1100;
int n, m;
bool x[MAXN], y[MAXN];
int main() {
  scanf("%d%d", &n, &m);
  int i;
  int recordx, recordy;
  for (i = 0; i < m; i++) {
    scanf("%d%d", &recordx, &recordy);
    x[recordx] = true;
    y[recordy] = true;
  }
  int ans = 0;
  for (i = 2; i < n; i++) {
    if (!x[i]) ans++;
    if (!y[i]) ans++;
  }
  if (n % 2 && !x[(n + 1) / 2] && !y[(n + 1) / 2]) ans--;
  printf("%d\n", ans);
  return 0;
}
