N = input()
E = '1'
X = 0
if N[0] != '1':
    X = -1

else:
    for i in range(len(N)):
        if int(E) == int(N):
            break
        if i == len(N) - 1:
            X = -1
            break

        E += '3'
        X += 1
    

print(X)