#include <bits/stdc++.h>
using namespace std;
int n, m;
bool row[1005], col[1005];
int main() {
  scanf("%d%d", &n, &m);
  for (int i = 1; i <= m; ++i) {
    int x, y;
    scanf("%d%d", &x, &y);
    row[x] = col[y] = true;
  }
  int ans = 0;
  for (int i = 2; i < n; ++i) {
    if (!row[i]) ++ans;
    if (!col[i]) ++ans;
  }
  if (n & 1 && !row[n / 2 + 1] && !col[n / 2 + 1]) --ans;
  printf("%d\n", ans);
  return 0;
}
