#include <bits/stdc++.h>
using namespace std;
template <class T>
void initvv(vector<vector<T> > &v, int a, int b, const T &t = T()) {
  v.assign(a, vector<T>(b, t));
}
template <class F, class T>
void convert(const F &f, T &t) {
  stringstream ss;
  ss << f;
  ss >> t;
}
char bx[1010], by[1010];
int main() {
  int n, m, x, y;
  scanf("%d%d", &n, &m);
  for (int i = 0; i < m; ++i) {
    scanf("%d%d", &x, &y);
    bx[x] = 1;
    by[y] = 1;
  }
  int ans = 0;
  for (int i = 2; i < n; ++i) {
    if (!bx[i]) {
      ++ans;
    }
    if (!by[i]) {
      ++ans;
    }
  }
  int k = n / 2 + 1;
  if (n % 2 == 1 && !bx[k] && !by[k]) {
    --ans;
  }
  printf("%d\n", ans);
}
