func_code_string: #include <bits/stdc++.h>   bool is_prime(int n) {     if (n < 2) {       return false;     }     for (int d = 2; d * d <= n; d++) {       if (n % d == 0) {         return false;       }     }     return true;   }   int main() {     int n;     std::cin >> n;     int m = n, cross = 0;     while (!is_prime(m + cross)) {       cross++;     }     assert(2 * cross <= n);     std::cout << m + cross << std::endl;     for (int i = 1; i <= n; i++) {       std::cout << i <<     << i % n + 1 << std::endl;     }     int jump = std::max(2, cross);     for (int i = 1; i <= cross; i++) {       assert(i < 1 + jump);       assert(i + jump <= n);       std::cout << i <<     << i + jump << std::endl;     }   }   