#include <stdio.h>
#include  <math.h>
int prime(int x);
int main()
{
	long n,i,j,max=0,a;
	scanf("%ld", &n);
	for (i = 2; i <= n; i++)
	{
		for (j = 2; j <= n; j++)
		{
			if (prime(i)&&prime(j)&&i+j==n)
			{
				a = i * j;
				if (max < i * j)
					max = i * j;
			}
		}
	}
	printf("%d", max);
	
	return 0;
}
int prime(int x)
{
	if (x == 1)return 0;
	if (x == 2)return 1;
	int k = 2;
	while (k * k <= x && x % k != 0)k++;
	if (x % k == 0) return 0;
	else return 1;
}