#include <bits/stdc++.h>
bool x[1010], y[1010];
int main() {
  int n, m;
  scanf("%d %d", &n, &m);
  int a, b;
  memset(x, true, sizeof(x));
  memset(y, true, sizeof(y));
  for (int i = 0; i < m; i++) {
    scanf("%d %d", &a, &b);
    x[a] = false;
    y[b] = false;
  }
  int ans = 0;
  for (int i = 2; i < n; i++) {
    if (x[i] || y[i]) ans++;
    if (x[i] && y[i] && (n % 2 == 0 || (n + 1) / 2 != i)) ans++;
  }
  printf("%d\n", ans);
  return 0;
}
