def f(x, a1, a2):
    return ((2540 <= x <= 8000) and (not (a1 <= x <= a2))) <= (4100 <= x <= 8230)


min_l = 10 ** 10
#254 409
for a1 in range(2340, 2600):
    for a2 in range(4000, 4150):
        if all(f(x, a1, a2) for x in range(1, 10000)):
            min_l = min(a2 - a1, min_l)

print(min_l / 10)#155.9 => 156