#include <bits/stdc++.h>
using namespace std;
bool usedi[2000], usedj[2000];
int main() {
  int n, m, i, j, br = 0;
  cin >> n >> m;
  for (i = 0; i < m; i++) {
    cin >> j;
    usedi[j] = 1;
    cin >> j;
    usedj[j] = 1;
  }
  if (n % 2 == 1 && usedi[n / 2 + 1] == 0 && usedj[n / 2 + 1] == 0)
    usedj[n / 2 + 1] = 1;
  for (i = 2; i < n; i++)
    if (usedi[i] == 0) br++;
  for (j = 2; j < n; j++)
    if (usedj[j] == 0) br++;
  cout << br << endl;
}
