text: #include <iostream>
  
  using namespace std;
  
  unsigned long long factorial(unsigned long long n);
  
  unsigned long long factorial(unsigned long long n){
      if (n == 0){
          return 1;
      }
      return n * factorial(n - 1);
  }
  
  int main(int argc, char *argv[]) {
      cout << factorial(10);
      
      return 0;
  }