#include <bits/stdc++.h>
using namespace std;
bool delhang[10002], dellie[10002];
int n, m, i, j, sum, x, y;
int main() {
  scanf("%d%d", &n, &m);
  for (i = 1; i <= m; ++i) {
    scanf("%d%d", &x, &y);
    delhang[x] = true;
    dellie[y] = true;
  }
  for (i = 2; i <= n - 1; ++i)
    if (!delhang[i]) sum++;
  for (i = 2; i <= n - 1; ++i)
    if (!dellie[i]) sum++;
  if (n % 2 == 1)
    if (!dellie[n / 2 + 1] && !delhang[n / 2 + 1]) sum--;
  printf("%d\n", sum);
}
