#include <bits/stdc++.h>
using namespace std;
bool row[1100], col[1100];
int main() {
  int n, m;
  while (scanf("%d %d", &n, &m) != EOF) {
    memset(row, true, sizeof(row));
    memset(col, true, sizeof(col));
    while (m--) {
      int x, y;
      scanf("%d %d", &x, &y);
      row[x] = false;
      col[y] = false;
    }
    int res = 0;
    for (int i = 2; i <= n - 1; i++) {
      if (n % 2 && i == n / 2 + 1) {
        continue;
      }
      if (col[i]) {
        res++;
      }
      if (row[i]) {
        res++;
      }
    }
    if (n % 2 && (col[n / 2 + 1] || row[n / 2 + 1])) {
      res++;
    }
    printf("%d\n", res);
  }
  return 0;
}
