n = int(input())
g = n // 8
y = n % 8
if y == 2 or y == 4 or y == 6:
    g = g + 1
elif y == 0:
    g = g
else:
    g = -1
if n == 2 or n == 4 or  n == 10:
    g = -1
print(g)