#include <bits/stdc++.h>
using namespace std;
int n, m;
int in[100005][3];
int x[1005], y[1005];
int main() {
  scanf("%d%d", &n, &m);
  for (int i = 2; i < n; ++i) x[i] = y[i] = 1;
  for (int i = 0; i < m; ++i) {
    scanf("%d%d", in[i], in[i] + 1);
    x[in[i][0]] = 0;
    y[in[i][1]] = 0;
  }
  int rez = 0;
  for (int i = 1; i <= n; ++i) rez += x[i] + y[i];
  if (n % 2 == 1)
    if (x[(1 + n) / 2] == 1 && y[(1 + n) / 2] == 1) --rez;
  printf("%d\n", rez);
  return 0;
}
