#include <stdio.h>

// Function to calculate factorial
unsigned long long calculateFactorial(int number) {
    if (number == 0 || number == 1) {
        return 1;
    } else {
        unsigned long long factorial = 1;
        while (number > 1) {
            factorial *= number;
            number--;
        }
        return factorial;
    }
}

int main() {
    int num;

    printf("Enter a positive integer: ");
    scanf("%d", &num);

    if (num < 0) {
        printf("Factorial is not defined for negative numbers.\n");
    } else {
        unsigned long long result = calculateFactorial(num);
        printf("Factorial of %d = %llu\n", num, result);
    }

    return 0;
}