#include <bits/stdc++.h>
using namespace std;
const int N = 2010;
int n, m, res;
bool a[N], f[N], g[N];
vector<int> v[N];
int main() {
  scanf("%d %d", &n, &m);
  for (int i = 2; i < n; i++) f[i] = g[i] = true;
  for (int i = 1; i <= m; i++) {
    int x, y;
    scanf("%d %d", &x, &y);
    f[x] = g[y] = false;
  }
  if (n & 1) {
    if (f[n / 2 + 1] || g[n / 2 + 1]) res++;
    f[n / 2 + 1] = g[n / 2 + 1] = false;
  }
  for (int i = 1; i <= n; i++) res += (int)f[i] + (int)g[i];
  printf("%d", res);
  return 0;
}
