func_code_string: #include <bits/stdc++.h>   using namespace std;   const int mx = 1e5 + 5;   int f[mx];   int32_t main() {     ios_base::sync_with_stdio(0);     cin.tie(0);     int n;     cin >> n;     vector<pair<int, int>> v;     for (int i = 3; 2 * i <= n; i += 2) {       if (f[i] == 0) {         int c = 0;         for (int j = i; j <= n; j += i) c += !f[j];         for (int j = i, l = -1; j <= n; j += i) {           if ((c & 1) && j == 2 * i) continue;           if (!f[j]) {             if (l == -1)               l = j;             else {               v.push_back({l, j});               l = -1;             }           }           f[j] = 1;         }       }     }     for (int j = 2, l = -1; j <= n; j += 2) {       if (!f[j]) {         if (l == -1)           l = j;         else {           v.push_back({l, j});           l = -1;         }       }     }     cout << v.size() <<   n ;     for (auto x : v) cout << x.first <<     << x.second <<   n ;   }   