T, S, D = map(int, input().split())
t = D / S
k = int(t // 24)
r = t % 24

total = k * 12.0

start = T
end = start + r

if end >= 24:
    # Split into two parts: start to 24, and 0 to end-24
    part1_start = start
    part1_end = 24.0
    overlap1 = max(0.0, part1_end - max(part1_start, 18.0))
    part2_end = end - 24.0
    overlap2 = max(0.0, min(part2_end, 6.0) - 0.0)
    total_overlap = overlap1 + overlap2
else:
    # Single part
    overlap1 = max(0.0, min(end, 24.0) - max(start, 18.0))
    overlap2 = max(0.0, min(end, 6.0) - max(start, 0.0))
    total_overlap = overlap1 + overlap2

total += total_overlap

print("{0:.15f}".format(total))