// shamelessly ukradeno iz
// https://www.geeksforgeeks.org/factorial-large-number/
// Maximum number of digits in output 
#include <stdio.h>
#include <stdlib.h>
#define MAX 5000 
int multiply(int x, int res[], int res_size); 

// This function finds factorial of large numbers 
// and prints them 
void factorial(int n) 
{ 
	int res[MAX]; 

	// Initialize result 
	res[0] = 1; 
	int res_size = 1; 

	// Apply simple factorial formula n! = 1 * 2 * 3 * 4...*n 
	for (int x=2; x<=n; x++) 
		res_size = multiply(x, res, res_size); 

	fprintf(stdout, "Factorial of given number is \n");
	for (int i=res_size-1; i>=0; i--) 
		fprintf(stdout, "%d", res[i]);
	fprintf(stdout, "\n");
} 

// This function multiplies x with the number  
// represented by res[]. 
// res_size is size of res[] or number of digits in the  
// number represented by res[]. This function uses simple  
// school mathematics for multiplication. 
// This function may value of res_size and returns the  
// new value of res_size 
int multiply(int x, int res[], int res_size) 
{ 
	int carry = 0;  // Initialize carry 

	// One by one multiply n with individual digits of res[] 
	for (int i=0; i<res_size; i++) 
	{ 
		int prod = res[i] * x + carry; 

		// Store last digit of 'prod' in res[]   
		res[i] = prod % 10;   

		// Put rest in carry 
		carry  = prod/10;     
	} 

	// Put carry in res and increase result size 
	while (carry) 
	{ 
		res[res_size] = carry%10; 
		carry = carry/10; 
		res_size++; 
	} 
	return res_size; 
} 

// Driver program 
int main(int argc, char ** argv) {
	if(argc != 2) {
		fprintf(stderr, "uporaba: %s stevilka\n", argv[0]);
		return 1;
	}
	factorial(atoi(argv[1])); 
	return 0; 
}