T, S, D = map(int, input().split())

distance = D - 0.5
travel_time = distance / S

if T < 18 and T + travel_time >= 18:  
    night_time = min(T + travel_time - 18, travel_time)  
    print("{:.10f}".format(night_time))
elif T >= 18 and T + travel_time >= 24:  
    night_time = min(T + travel_time - 24 + 6, travel_time)  
    print("{:.10f}".format(night_time))
else:  
    print(0)