#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  int m;
  cin >> n >> m;
  vector<bool> legalX(n, true);
  vector<bool> legalY(n, true);
  legalX[0] = false;
  legalX[n - 1] = false;
  legalY[0] = false;
  legalY[n - 1] = false;
  for (int i = 0; i < m; i++) {
    int bX;
    int bY;
    cin >> bX >> bY;
    legalX[bX - 1] = false;
    legalY[bY - 1] = false;
  }
  int bestScore = 0;
  for (int i = 1; i < n / 2; i++) {
    int count = 0;
    if (legalX[i]) count++;
    if (legalY[i]) count++;
    if (legalX[n - 1 - i]) count++;
    if (legalY[n - 1 - i]) count++;
    bestScore += count;
  }
  if (n % 2 == 1) {
    if (legalX[n / 2] || legalY[n / 2]) bestScore++;
  }
  cout << bestScore << endl;
  return 0;
}
