P = [i for i in range(130, 190 + 1)]
Q = [i for i in range(170, 230 + 1)]


def f(x, a1, a2):
    return (not ((x not in P) <= (x in Q))) <= ((a1 <= x <= a2) <= ((x not in Q) <= (x in P)))

max_l = 0
for a1 in range(100, 250):
    for a2 in range(a1 + 1, 250):
        if all(f(x, a1, a2) for x in range(-1000, 1000)):
            max_l = max(max_l, a2 - a1)

print(max_l/ 10)