func_code_string: #include <bits/stdc++.h>   using namespace std;   const long long MAX_N = 10 * 100 + 19;   const long long inf = 2e9 + 19;   long long n;   int32_t main() {     ios::sync_with_stdio(false), cin.tie(0), cout.tie(0);     cin >> n;     cout << 1ll * ((n + 1) / 2) * (n / 2) << endl;     for (long long i = 1; i <= n; i++)       for (long long j = i + 1; j <= n; j++)         if ((i & 1) != (j & 1)) cout << i <<     << j << endl;     return (0);   }   