a =  input()
a = int(a)
num_range = range(a, 2*a+1)
list1=[]
for x in range(2,2*a+1):
    for y in range(2,2*a+1):
        if x*y in num_range:
            z = x*y
            list1.append(z)
        else:
            continue
if len(list1)== 0:
    print(-1)
else:
    print(list1[0])