#include <bits/stdc++.h>
using namespace std;
int b[1007][1007];
bool xc[1007], xu[1007], yc[1007], yu[1007];
bool fxc[1007];
int main() {
  int n, m;
  scanf("%d %d", &n, &m);
  int x, y;
  for (int i = 2; i <= n - 1; i++) {
    xc[i] = true;
    xu[i] = true;
    yc[i] = true;
    yu[i] = true;
  }
  for (int i = 1; i <= m; i++) {
    scanf("%d %d", &x, &y);
    yu[y] = yc[y] = false;
    xu[x] = xc[x] = false;
  }
  int ans = 0;
  for (int i = 2; i <= n / 2; i++) {
    if (xc[i]) ans++;
    if (yc[i]) ans++;
    if (xc[n + 1 - i]) ans++;
    if (yc[n + 1 - i]) ans++;
  }
  if (n % 2) {
    if (xc[n / 2 + 1] || yc[n / 2 + 1]) ans++;
  }
  printf("%d ", ans);
  return 0;
}
