#include <bits/stdc++.h>
using namespace std;
bool gridr[1005];
bool gridc[1005];
int main() {
  int n, m, x, y;
  scanf("%d %d", &n, &m);
  memset(gridr, true, sizeof(gridr));
  memset(gridc, true, sizeof(gridc));
  gridr[1] = false;
  gridr[n] = false;
  gridc[1] = false;
  gridc[n] = false;
  for (int i = 0; i < m; i++) {
    scanf("%d %d", &x, &y);
    gridr[x] = false;
    gridc[y] = false;
  }
  if (n & 1 && gridr[n / 2 + 1]) gridc[n / 2 + 1] = false;
  int ret = 0;
  for (int i = 1; i <= n; i++) {
    ret += gridr[i] + gridc[i];
  }
  printf("%d\n", ret);
  return 0;
}
