#include <bits/stdc++.h>
using namespace std;
const int maxn = 1010;
bool usedx[maxn], usedy[maxn];
int main() {
  int n, m;
  scanf("%d%d", &n, &m);
  for (int i = 0; i < m; ++i) {
    int x, y;
    scanf("%d%d", &x, &y);
    --x;
    --y;
    usedx[x] = 1;
    usedy[y] = 1;
  }
  int Count = 0;
  for (int i = 1; i < n - 1; ++i) {
    Count += !usedx[i];
    Count += !usedy[i];
  }
  if (n % 2 == 1 && usedx[n / 2] == 0 && usedy[n / 2] == 0) {
    --Count;
  }
  printf("%d", Count);
}
