N = int(eval(input()))

import math



for x in range(900000 + 1):

    if math.floor(x * 1.08) == N:

        print(x)

        break

else:

    print(':(')
N = int(eval(input()))

import math



x = math.ceil(N / 1.08)

print((str(x) if math.floor(x * 1.08) == N else ':('))
N = int(eval(input()))
import math

for x in range(900000 + 1):
    if math.floor(x * 1.08) == N:
        print(x)
        break
else:
    print(":(")

N = int(eval(input()))
import math

x = math.ceil(N / 1.08)
print((str(x) if math.floor(x * 1.08) == N else ":("))

-for x in range(900000 + 1): -    if math.floor(x * 1.08) == N: -        print(x) -        break -else: -    print(":(") +x = math.ceil(N / 1.08) +print((str(x) if math.floor(x * 1.08) == N else ":("))