#include <bits/stdc++.h>
using namespace std;
int main(int argc, char const *argv[]) {
  set<int> rows, cols;
  int N, M;
  scanf("%d %d", &N, &M);
  for (int i = 1; i < N - 1; ++i) {
    rows.insert(i + 1);
    cols.insert(i + 1);
  }
  for (int i = 0; i < M; ++i) {
    int row, col;
    scanf("%d %d", &row, &col);
    rows.erase(row);
    cols.erase(col);
  }
  int all = ((int)((rows).size())) + ((int)((cols).size()));
  if (N % 2 && rows.find((N + 1) / 2) != rows.end() &&
      cols.find((N + 1) / 2) != cols.end()) {
    all--;
  }
  printf("%d\n", all);
  return 0;
}
