Let the probability of getting head for a biased coin be \( \dfrac{1}{4} \). It is tossed repeatedly until a head appears. Let \( N \) be the number of tosses required. If the probability that the equation \( 64x^2 + 5Nx + 1 = 0 \) has no real root is \( \dfrac{p}{q} \), where \( p \) and \( q \) are coprime, then \( q - p \) is equal to _______.
