big integers c++ prime factors p,q

i need to do this within 24 hours. You are given a number n that is known to be composite. Furthermore, n=p*q for two prime factors p,q. Your goal is to find the prime factor. A list of numbers will be provided to winner to help test and calibrate your code. Each number in the list must be factored in under a minute.(It should handle 20 digit numbers in under 30 seconds)