n=int(input())
ans=0

for i in range(n-n%2,max(n-15,0),-2):
    a=int(pow(i,0.5))
    for j in range(int(pow(a,0.5)),a+1):
        if i%j==0:
            if n >= (i//j)*2 + j*2:
                ans=max((i//j)*j,ans)
           
print(ans)