/****************************************************************************
 * fs1.c
 *
 * Computer Science 50
 * David J. Malan
 *
 * Computes n'th Fibonacci number.
 *
 * Demonstrates recursion (and bad design).
 ***************************************************************************/
       
#include <cs50.h>
#include <stdio.h>
#include <stdlib.h>


/* prototype */
long long fs(int);


int
main(int argc, char * argv[])
{
    int n;

    /* ensure proper usage */
    if (argc != 2)
    {
        printf("Usage: %s n\n", argv[0]);
        return 1;
    }

    /* compute and print n'th number in Fibonacci sequence */
    n = atoi(argv[1]);
    if (n < 0)
        printf("Input must be non-negative.\n");
    else
        printf("fs(%d) = %lld\n", n, fs(n));
}


/*
 * long long
 * fs(int n)
 *
 * Returns n'th number in Fibonacci sequence.
 */

long long
fs(int n)
{
    /* compute n'th number */
    if (n == 0)
        return 0;
    else if (n == 1)
        return 1;
    else
        return (fs(n-1) + fs(n-2));
}