/*
 * Factorial using recursive method
 */
import std.stdio;

real factorial(uint i) {
	if (i == 0) {
		return 1;
	} else {
		return factorial(i - 1) * i;
	}
}

int main()
{
    writef("Enter an unsigned int: ");
	uint i = 0;
	
	scanf("%u", &i);
	
	writefln(factorial(i));

    return 0;
}