N=int(eval(input()))

ans = -1



for i in range(50000+10):

 x1 = int(i*1.08)

 x2 = i*1.08

 #print(i,x1,x2)

 if(x1 == N): ans = i

 elif(x2 == N): ans = i

  

  

if(ans == -1):

 print(':(')

else:

 print(ans)
N = int(eval(input()))



ans = -1

for x in range(N+1):

  if(int(x*1.08) == N):

    ans = x

    break

    

if(ans == -1): print(':(')

else: print(ans)

N = int(eval(input()))
ans = -1
for i in range(50000 + 10):
    x1 = int(i * 1.08)
    x2 = i * 1.08
    # print(i,x1,x2)
    if x1 == N:
        ans = i
    elif x2 == N:
        ans = i
if ans == -1:
    print(":(")
else:
    print(ans)

N = int(eval(input()))
ans = -1
for x in range(N + 1):
    if int(x * 1.08) == N:
        ans = x
        break
if ans == -1:
    print(":(")
else:
    print(ans)

-for i in range(50000 + 10): -    x1 = int(i * 1.08) -    x2 = i * 1.08 -    # print(i,x1,x2) -    if x1 == N: -        ans = i -    elif x2 == N: -        ans = i +for x in range(N + 1): +    if int(x * 1.08) == N: +        ans = x +        break