import sys

import numpy as np

sys.setrecursionlimit(10 ** 9)



stdin = sys.stdin

 

ri = lambda: int(rs())

rl = lambda: list(map(int, stdin.readline().split()))

rs = lambda: stdin.readline().rstrip()  # ignore trailing spaces



N = ri()

x = N // 1.08

bool = True

if int(x * 1.08) != N or x < 1:

    x += 1

    if int(x * 1.08) != N:

        bool = False

print((int(x) if bool else ':('))

import sys

import math



stdin = sys.stdin

 

ri = lambda: int(rs())

rl = lambda: list(map(int, stdin.readline().split()))

rs = lambda: stdin.readline().rstrip()  # ignore trailing spaces



N = ri()

x = math.ceil(N / 1.08)

bool = True

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

    bool = False

print((int(x) if bool else ':('))

import sys
import numpy as np

sys.setrecursionlimit(10**9)
stdin = sys.stdin
ri = lambda: int(rs())
rl = lambda: list(map(int, stdin.readline().split()))
rs = lambda: stdin.readline().rstrip()  # ignore trailing spaces
N = ri()
x = N // 1.08
bool = True
if int(x * 1.08) != N or x < 1:
    x += 1
    if int(x * 1.08) != N:
        bool = False
print((int(x) if bool else ":("))

import sys
import math

stdin = sys.stdin
ri = lambda: int(rs())
rl = lambda: list(map(int, stdin.readline().split()))
rs = lambda: stdin.readline().rstrip()  # ignore trailing spaces
N = ri()
x = math.ceil(N / 1.08)
bool = True
if math.floor(x * 1.08) != N:
    bool = False
print((int(x) if bool else ":("))

-import numpy as np +import math -sys.setrecursionlimit(10**9) -x = N // 1.08 +x = math.ceil(N / 1.08) -if int(x * 1.08) != N or x < 1: -    x += 1 -    if int(x * 1.08) != N: -        bool = False +if math.floor(x * 1.08) != N: +    bool = False