func_code_string: #include <bits/stdc++.h>   using namespace std;   const long long int MOD = 1000000007;   const long double PI = 2 * acos(0.0);   const vector<long long int> dx = {1, -1, 0, 0};   const vector<long long int> dy = {0, 0, 1, -1};   vector<long long int> ga(long long int n, bool oneIndexed = false) {     vector<long long int> a;     if (oneIndexed) a.push_back(0ll);     for (long long int i = 0; i < n; i++) {       long long int p;       cin >> p;       a.push_back(p);     }     return move(a);   }   vector<unsigned long long int> gau(unsigned long long int n,                                      bool oneIndexed = false) {     vector<unsigned long long int> a;     if (oneIndexed) a.push_back(0llu);     for (unsigned long long int i = 0; i < n; i++) {       unsigned long long int p;       cin >> p;       a.push_back(p);     }     return move(a);   }   vector<string> gas(unsigned long long int n, bool oneIndexed = false) {     vector<string> a;     if (oneIndexed) a.push_back(  );     for (unsigned long long int i = 0; i < n; i++) {       string p;       cin >> p;       a.push_back(p);     }     return move(a);   }   template <typename T, typename A>   void pa(vector<T, A> const &a, long long int begin = 0,           long long int end = -1) {     if (end == -1) end = a.size() - 1;     for (long long int i = begin; i <= end; i++) {       cout << a[i] <<    ;     }     cout <<   n ;   }   template <typename T, typename A>   void papair(vector<T, A> const &a, long long int begin = 0,               long long int end = -1) {     if (end == -1) end = (long long int)a.size() - 1;     for (long long int i = begin; i <= end; i++) {       cout << a[i].first <<     << a[i].second <<   n ;     }     cout <<   n ;   }   void yes() { cout <<  YES n ; }   void no() { cout <<  NO n ; }   void yesno(int f) {     if (f)       yes();     else       no();   }   void solve() {     long long int n;     cin >> n;     vector<pair<long long int, long long int>> edges;     long long int p1 = n / 2, p2 = n / 2;     if (p1 + p2 < n) p2++;     for (long long int i = 1; i <= p1; i++) {       for (long long int j = p1 + 1; j <= n; j++) {         edges.push_back({i, j});       }     }     cout << (long long int)edges.size();     cout <<   n ;     papair(edges);   }   int main(void) {     ios::sync_with_stdio(0);     cin.tie(0);     cout.tie(0);     solve();     return 0;   }   