/* standard library includes */
#include<stdio.h>

/* the function prototype */
int f(int, int);

/* the main function with the default arguments */
int main(int argc, char **argv)
{
    /* declare x, y and result to save the numbers */
    int x, y, result;

    /* ask for the numbers */
    printf("Enter number for x and y separated by a space:\n");
    scanf("%d %d", &x, &y);

    /* calculate the result */
    result = f(x, y);

    /* print the result */
    printf("The result is: %d\n", result);

    /* exit the program */
    return 0;
}

/* the function body */
int f(int x, int y)
{
    /* return if x<0 or y<0 */
    if(x<0 || y<0)
    {
        return x-y;
    }
    /* else recurse until we get x or y < 0 */
    else
    {
        return f(x-1, y) + f(x, y-1);
    }
}