#include <bits/stdc++.h>
using namespace std;
int c[10000] = {0}, d[10000] = {0};
int main() {
  int n, m, i;
  scanf("%d%d", &n, &m);
  for (i = 0; i < m; i++) {
    int x, y;
    scanf("%d%d", &x, &y);
    c[x]++;
    d[y]++;
  }
  int ans = 0, j, kc = 0, kd = 0;
  for (i = 2; i <= n - 1; i++) {
    if (!c[i]) ans++;
    if (!d[i]) ans++;
  }
  if (n % 2 == 1 && !c[(n + 1) / 2] && !d[(n + 1) / 2]) ans--;
  printf("%d\n", ans);
  return 0;
}
