N = int(eval(input()))



for a in range(0, N+1):

    if int(a * 1.08) == N:

        print(a)

        break



else:

    print(':(')

N = int(eval(input()))

X = int(N / 1.08)



for x in range(X - 1, X + 2):

    if int(x * 1.08) == N:

        print(x)

        break

else:

    print(':(')

N = int(eval(input()))
for a in range(0, N + 1):
    if int(a * 1.08) == N:
        print(a)
        break
else:
    print(":(")

N = int(eval(input()))
X = int(N / 1.08)
for x in range(X - 1, X + 2):
    if int(x * 1.08) == N:
        print(x)
        break
else:
    print(":(")

-for a in range(0, N + 1): -    if int(a * 1.08) == N: -        print(a) +X = int(N / 1.08) +for x in range(X - 1, X + 2): +    if int(x * 1.08) == N: +        print(x)