import sys

N = int(eval(input()))

for i in range(N+1):

    a = int(i * 1.08)

    if N == a:

        print(i)

        sys.exit()

print(':(')
import math

n = int(eval(input()))

a = math.ceil(n/1.08)

if int(a*1.08) == n:

    print(a)

else:

    print(':(')
import sys

N = int(eval(input()))
for i in range(N + 1):
    a = int(i * 1.08)
    if N == a:
        print(i)
        sys.exit()
print(":(")

import math

n = int(eval(input()))
a = math.ceil(n / 1.08)
if int(a * 1.08) == n:
    print(a)
else:
    print(":(")

-import sys +import math -N = int(eval(input())) -for i in range(N + 1): -    a = int(i * 1.08) -    if N == a: -        print(i) -        sys.exit() -print(":(") +n = int(eval(input())) +a = math.ceil(n / 1.08) +if int(a * 1.08) == n: +    print(a) +else: +    print(":(")