#include <bits/stdc++.h>
#pragma comment(linker, "/STACK:100000000")
using namespace std;
const double pi = acos(-1.0);
const int size = 2000;
bool used1[size], used2[size];
int main() {
  int n, m, x, y;
  scanf("%d%d", &n, &m);
  for (int i = 0; i < n; i++) {
    used1[i] = true;
    used2[i] = true;
  }
  for (int i = 0; i < m; i++) {
    scanf("%d%d", &x, &y);
    x--, y--;
    used1[x] = false;
    used2[y] = false;
  }
  int ans = 0;
  if (n & 1) {
    ans += used1[n / 2] || used2[n / 2];
  }
  for (int i = 1; i < n / 2; i++) {
    ans += used1[i] + used2[i] + used1[n - i - 1] + used2[n - i - 1];
  }
  cout << ans << endl;
  return 0;
}
