N = input()
E = '1'
X = 0
for i in range(len(N)):
    if i == 0:
        if N[0] != '1':
            X = -1
            break
    elif i == len(N) - 1:
        X = -1
        break
    

    E += '3'
    X += 1
    if int(E) == int(N):
        break
    

print(X)