#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, m, i, a, b, s = 0, r[1005] = {0}, c[1005] = {0};
  scanf("%d%d", &n, &m);
  while (m--) scanf("%d%d", &a, &b), r[a] = 1, c[b] = 1;
  for (i = 2; i < n; i++) s += !r[i] + !c[i];
  if ((n & 1) && !r[(n + 1) / 2] && !c[(n + 1) / 2]) s--;
  printf("%d", s);
  return 0;
}
