n=int(eval(input()));print((([m for m in range(n+1)if int(m*1.08)==n]+[':('])[0]))
n=int(eval(input()))+1;print((n%27%14and int(n/1.08)or':('))
n = int(eval(input()))
print((([m for m in range(n + 1) if int(m * 1.08) == n] + [":("])[0]))

n = int(eval(input())) + 1
print((n % 27 % 14 and int(n / 1.08) or ":("))

-n = int(eval(input())) -print((([m for m in range(n + 1) if int(m * 1.08) == n] + [":("])[0])) +n = int(eval(input())) + 1 +print((n % 27 % 14 and int(n / 1.08) or ":("))