#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  scanf("%d", &n);
  int m;
  scanf("%d", &m);
  vector<int> r(n, 0), c(n, 0);
  int i, j;
  for (i = 0; i < m; i++) {
    int x;
    scanf("%d", &x);
    int y;
    scanf("%d", &y);
    r[x - 1] = 1;
    c[y - 1] = 1;
  }
  int ans = 0;
  for (i = 1; i < n - 1; i++) {
    if (r[i] == 0 || c[i] == 0) ans++;
    if (r[i] == 0 && c[i] == 0 && i != n - 1 - i) ans++;
  }
  printf("%d\n", ans);
}
