#include <stdio.h>

int factorial(int number);

int main() {
    printf("0! = %i\n", factorial(0));
    printf("1! = %i\n", factorial(1));
    printf("3! = %i\n", factorial(3));
    printf("5! = %i\n", factorial(5));
}

int factorial(int number) {
    if (number > 1) {
        return number * factorial(number-1);
    }
    else {
        return 1;
    }
}