T, S, D = map(int, input().split())
total_time = D / S
T_end = T + total_time

k_max = int((T_end - 18) // 24)
total_careful = 0.0

for k in range(k_max + 1):
    s1 = 24 * k + 18
    e1 = 24 * k + 24
    a = max(T, s1)
    b = min(T_end, e1)
    if a < b:
        total_careful += b - a
    
    s2 = 24 * k + 24
    e2 = 24 * k + 30
    a = max(T, s2)
    b = min(T_end, e2)
    if a < b:
        total_careful += b - a

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