def is_prime(n):
if n <= 1:
return False
if n == 2:
return True
if n % 2 == 0:
return False
for i in range(3, int(n**0.5) + 1, 2):
if n % i == 0:
return False
return True
x = int(input())
found = -1
for num in range(x, 2 * x + 1):
if num > 1 and not is_prime(num):
found = num
break
print(found)

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