n=int(input())
s=0
def su(t):
	k=0
	for i in range(2,t):
		if t%i==0:
			k=1
			break
	if k==0:
		return True
	else:
		return False
for i in  range(2,n):
    for j in range(2,n):
        if((su(i))and(su(j)))and(i*j==n):
           s=max(i,j)
print(s)