If the number is prime, then only 1 has to be paid. That is the minimum possible. The next minimum is 2. Since the Goldbach conjecture has been verified upto the limit, we can use it. Any even number is the sum of two primes. We don't need to actually find the pair of primes, we just know it exists. If a number is odd and composite , n = (n-2) + 2, is the only way it can be written as the sum