def is_prime(S): primes=[2] flag=True for i in range(3,S): for j in range(2,i): if i%j==0: flag=False break else: primes.append(i) return primes def ji_max(primes): ji_results=[] for prime in primes: if (S-prime)in primes: ji=prime*(S-prime) ji_results.append(ji) return max(ji_results) S=int(input()) primes=is_prime(S) print(ji_max(primes))