#include <bits/stdc++.h>
bool cantx[1001], canty[1001];
int main() {
  int i, j, k;
  int n, m, cnt = 0;
  scanf("%d%d", &n, &m);
  while (m--) {
    scanf("%d%d", &i, &j);
    cantx[i] = 1;
    canty[j] = 1;
  }
  for (i = 2; i <= n - 1; i++) {
    if (!cantx[i]) cnt++;
    if (!canty[i]) cnt++;
  }
  if (n % 2 && !cantx[n / 2 + 1] && !canty[n / 2 + 1]) {
    cnt--;
  }
  printf("%d\n", cnt);
}
