func_code_string: #include <bits/stdc++.h>   using namespace std;   const int MAXN = 1000;   bool g[MAXN][MAXN];   bool mh[MAXN], mv[MAXN];   bool use[MAXN];   int main() {     int n, m;     cin >> n >> m;     for (int i = 0; i < m; i++) {       int a, b;       cin >> a >> b;       a--;       b--;       g[a][b] = true;       mv[a] = true;       mh[b] = true;     }     int ans = 0;     for (int i = 1; i < n - 1; i++) ans += !mh[i] + !mv[i];     if (n % 2 && !mh[n / 2] && !mv[n / 2]) ans--;     cout << ans << endl;     return 0;   }   