#include <bits/stdc++.h>
using namespace std;
const int inv = numeric_limits<int>::max();
const int minv = numeric_limits<int>::min();
const int max_n = 1010;
int n, m;
bool R[max_n];
bool C[max_n];
int main() {
  scanf("%d", &n);
  scanf("%d", &m);
  fill(R, R + n, true);
  fill(C, C + n, true);
  for (int i = 0; i < m; ++i) {
    int ci, cj;
    scanf("%d", &ci);
    scanf("%d", &cj);
    --ci;
    --cj;
    R[ci] = false;
    C[cj] = false;
  }
  int q = 0;
  for (int i = 1; i < n - 1; ++i) q += R[i];
  for (int j = 1; j < n - 1; ++j) q += C[j];
  if (n % 2 == 1 and R[n / 2] and C[n / 2]) --q;
  printf("%d\n", q);
  return 0;
}
