import math

n = int(eval(input()))

ans = math.ceil(n/1.08)

if math.floor((math.ceil(n/1.08))*1.08) != n:

    ans = ':('

print(ans)
import math

n = int(eval(input()))

x1 = math.ceil(n/1.08)

print((':(' if math.floor(x1*1.08) != n else x1))
import math

n = int(eval(input()))
ans = math.ceil(n / 1.08)
if math.floor((math.ceil(n / 1.08)) * 1.08) != n:
    ans = ":("
print(ans)

import math

n = int(eval(input()))
x1 = math.ceil(n / 1.08)
print((":(" if math.floor(x1 * 1.08) != n else x1))

-ans = math.ceil(n / 1.08) -if math.floor((math.ceil(n / 1.08)) * 1.08) != n: -    ans = ":(" -print(ans) +x1 = math.ceil(n / 1.08) +print((":(" if math.floor(x1 * 1.08) != n else x1))