#include <bits/stdc++.h>
using namespace std;
int n, m, i, x, y, ans = 0, t;
bool p1[1010], p2[1010];
int main() {
  scanf("%d%d", &n, &m);
  for (i = 1; i <= n; i++) p1[i] = p2[i] = 1;
  p1[1] = p2[1] = p1[n] = p2[n] = 0;
  for (i = 1; i <= m; i++) {
    scanf("%d%d", &x, &y);
    p1[x] = p2[y] = 0;
  }
  ans = 2 * (n - 2);
  for (i = 2; i < n; i++) {
    if (p1[i] == 0) ans--;
    if (p2[i] == 0) ans--;
  }
  if (n % 2) {
    t = n / 2 + 1;
    if (p1[t] == 0) ans++;
    if (p2[t] == 0) ans++;
    ans -= 2;
    if (p1[t] || p2[t]) ans++;
  }
  cout << ans << endl;
  return 0;
}
