#include <bits/stdc++.h>
using namespace std;
const int OO = 1e9;
const long long INF = 1e18;
const int irand(int lo, int hi) {
  return ((double)rand() / (RAND_MAX + 1.0)) * (hi - lo + 1) + lo;
}
const long long lrand(long long lo, long long hi) {
  return ((double)rand() / (RAND_MAX + 1.0)) * (hi - lo + 1) + lo;
}
template <typename T>
T getnum() {
  int sign = 1;
  T ret = 0;
  char c;
  do {
    c = getchar();
  } while (c == ' ' || c == '\n');
  if (c == '-')
    sign = -1;
  else
    ret = c - '0';
  while (1) {
    c = getchar();
    if (c < '0' || c > '9') break;
    ret = 10 * ret + c - '0';
  }
  return sign * ret;
}
inline void ini(int& x) { x = getnum<int>(); }
inline void scani(int& x) { scanf("%d", &x); }
inline void OPTIMIZE() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
}
const int N = 1005;
int n, m;
int xx[N];
int yy[N];
int main() {
  OPTIMIZE();
  cin >> n >> m;
  for (int i = 1; i <= m; i += 1) {
    int x, y;
    cin >> x >> y;
    xx[x] = 1;
    yy[y] = 1;
  }
  int ans = 0;
  for (int i = 2; i <= n - 1; i += 1) {
    if (!xx[i]) ans++;
    if (!yy[i]) ans++;
    if ((n & 1) && i == n / 2 + 1 && !xx[i] && !yy[i]) ans--;
  }
  cout << ans << '\n';
  return 0;
}
