#include <bits/stdc++.h>
int n, m, garo[1111], sero[1111];
int main() {
  scanf("%d%d", &n, &m);
  int x, y;
  for (int i = 1; i <= m; i++) {
    scanf("%d%d", &x, &y);
    garo[x] = 1;
    sero[y] = 1;
  }
  garo[1] = garo[n] = sero[1] = sero[n] = 1;
  int sol = 0;
  for (int i = 1; i <= n; i++) {
    if (!garo[i] || !sero[i]) {
      if ((i == (n / 2 + 1)) && ((n % 2) == 1)) {
        sol++;
      } else {
        sol += !garo[i];
        sol += !sero[i];
      }
    }
  }
  printf("%d\n", sol);
  return 0;
}
