def eiler_func(p, q):
    """
    Computes Euler's totient function for the modulus 'n' computed as `p`*`q`.
    
    Args:
        p (long): First modulus factor.
        q (long): Second modulus factor.
    
    Returns:
        long: Euler's totient function value for the modulus n=`p`*`q`.
    """
    
    phi = (p - 1) * (q - 1)
    return phi