#include <bits/stdc++.h>
using namespace std;
const double pi =
    3.141592653589793238462643383279502884197169399375105820974944592307816406286208998628034825342;
bool badR[1010], badC[1010];
int main() {
  int n, m;
  scanf("%d%d", &n, &m);
  for (int i = 0; i < (m); ++i) {
    int x, y;
    scanf("%d%d", &x, &y);
    x--;
    y--;
    badR[x] = 1;
    badC[y] = 1;
  }
  int res = 0;
  for (int i = (1); i < (n / 2); ++i) {
    res += !badR[i];
    res += !badR[n - 1 - i];
    res += !badC[i];
    res += !badC[n - 1 - i];
  }
  if (n % 2 && (!badC[n / 2] || !badR[n / 2])) res++;
  printf("%d\n", res);
  return 0;
}
