#include
unsigned long long factorial(int n) { if (n <= 1) { return 1; } return n * factorial(n - 1); }
int main() { int num; std::cout << "Enter a number: "; std::cin >> num;
if (num < 0) {
std::cout << "Factorial is not defined for negative numbers." << std::endl;
} else {
unsigned long long result = factorial(num);
std::cout << "Factorial of " << num << " is " << result << std::endl;
}
return 0;
}