Finding (p-1)(q-1) with good precision from the product pq of two positive integers p and q is highly challenging, especially if p and q are primes, due to the complexity of prime factorization. For large values of p and q, (p-1)(q-1) approximates 0.9999 times pq, but achieving precise calculations remains elusive. If p and q are not prime, the approximation still holds, but the precision is limited. The difference between pq and (p-1)(q-1) can be estimated based on the magnitudes of p and q, particularly when they are close to the geometric mean of pq. Overall, while rough approximations can be made, they may not be useful for cryptographic applications.