#include <bits/stdc++.h>
using namespace std;
void debug() {
  fflush(stdin);
  printf("Press any key to continue");
  getc(stdin);
  fflush(stdin);
}
int n;
int m;
int r[1005], c[1005];
int main() {
  scanf("%d%d", &n, &m);
  for (int i = 1; i <= n; i++) {
    r[i] = 1;
    c[i] = 1;
  }
  while (m--) {
    int x, y;
    scanf("%d%d", &x, &y);
    r[x] = 0;
    c[y] = 0;
  }
  int ans = 0;
  for (int i = 2; i <= n / 2; i++)
    ans = ans + r[i] + r[n - i + 1] + c[i] + c[n - i + 1];
  if (n & 1) ans = ans + min(1, r[(n + 1) / 2] + c[(n + 1) / 2]);
  printf("%d\n", ans);
  return 0;
}
