a=int(input())

if a>=90:

    print(4.0)

elif 60<=a<90:

 	k=(90-a)/10
 	print(4.0-k)

else: s=a**0.5*10

if s>=60:
    k=4.0-(90-a)/10
    print("%.1f"%k)

else:
    print(0.0)