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