defen = int(input())
if(defen >= 90) :
    print("4.0")
elif(defen > 60) :
    print(4.0 - (90 - defen) / 10)
else :
    defen = float(pow(defen, 0.5) * 10)
    if(defen < 60) :
        print("0.0")
    else :
        print((4.0 - (90 - defen) / 10))