def f(x, a1, a2):
    return ((590 <= x <= 2280) <= (a1 <= x <= a2)) or (
            ((x % 30 == 0) <= (2570 <= x <= 3560)) <= ((50 <= x <= 6000) <= (a1 <= x <= a2)))


min_l = 10 ** 10
for a1 in range(550, 590):
    for a2 in range(2000, 2300):
        if all(f(x, a1, a2) for x in range(1, 5000)):
            min_l = min(a2 - a1, min_l)

print(min_l/10)