Takahashi bought a piece of apple pie at ABC Confiserie. According to his memory, he paid N yen (the currency of Japan) for it.  The consumption tax rate for foods in this shop is 8 percent. That is, to buy an apple pie priced at X yen before tax, you have to pay X \times 1.08 yen (rounded down to the nearest integer).  Takahashi forgot the price of his apple pie before tax, X, and wants to know it again. Write a program that takes N as input and finds X. We assume X is an integer.  If there are multiple possible values for X, find any one of them. Also, Takahashi's memory of N, the amount he paid, may be incorrect. If no value could be X, report that fact.
N = int(input())
for X in range(int(N/1.1), N):
    if int(X * 10.8) == N:
        print(X)
        exit()
print(":(")

N = int(input())
for X in [-int(-N/1.08), int((N+1)/1.08)]:
    if int(X * 1.08) == N:
        print(X)
        exit()
print(":(")
