Q10375: Choose and divide

/*
    exp(x) return a double, so we have to convert its datatype to long double
    long double: printf("%Lf"), scanf("%LF")

    Run time: 0.056
*/
#include <stdio.h>
#include <math.h>

long double compute(int m, int n);

int main()
{
    int p, q, r, s;
    long double tmp1, tmp2, result;


    while (scanf("%d%d%d%d", &p, &q, &r, &s) == 4)
    {
        if (2*q > p)
            q = p - q;
        if (2*s > r)
            s = r - s;

        if (!q) tmp1 = 0;
        else    tmp1 = compute(p, q);

        if (!s) tmp2 = 0;
        else    tmp2 = compute(r, s);

        result = exp(tmp1-tmp2);

        printf("%.5Lf\n", result);
    }

    return 0;
}

long double compute(int m, int n)
{
    int i;
    long double tmp = 0;

    for ( i = 1; i <= m; i++)
        tmp += log(i);

    for ( i = 1; i <= n; i++)
        tmp -= log(i);

    for ( i = 1; i <= (m-n); i++)
        tmp -= log(i);

    return tmp;

}