public static int f(int n) {
int prod = 1;
while (n > 1) {
prod = prod * n;
n = n - 2;
}
return prod;
}
    public static int fRec(int n){
        return recHelp(n, 1);
    }
    public static int recHelp(int n,int prod){
        if (n > 1) {
            prod = prod * n;
            n = n - 2;
            return recHelp(n, prod);
        }
        return prod;
    }