#include <bits/stdc++.h>
using namespace std;
bool visx[1100], visy[1100];
int main() {
  int N, M;
  scanf("%d%d", &N, &M);
  memset(visx, 0, sizeof(visx));
  memset(visy, 0, sizeof(visy));
  while (M--) {
    int t1, t2;
    scanf("%d%d", &t1, &t2);
    visx[t1] = 1;
    visy[t2] = 1;
  }
  int ans = 0;
  for (int i = 2; i < N; i++) {
    if (!visx[i]) ans++;
    if (!visy[i]) ans++;
  }
  if (N % 2) {
    int mid = N / 2 + 1;
    if (!visx[mid] && !visy[mid]) ans--;
  }
  printf("%d\n", ans);
  return 0;
}
