import math

def A1(s):
    if s<0:
        return -1
    elif s<60:
        return (1.0/(math.e**(60 - math.fabs(s))))
    else:
        return 1.0


def A2(s):
    if s<0:
        return -1
    elif s<=10:
        return 1.0
    else:
        return (1.0/(1.0 + math.e**(math.fabs(10-s))))


def B1(s):
    if s<0:
        return -1
    elif s >=0 and s<=0.8:
        return (1.0/(1.0+(0.2+s)**3))
    else:
        return 1.0


def B2(s):
    if s<0:
        return -1
    elif s >=0 and s<= 0.1:
        return 1.0
    else:
        return (1.0/(1.0 + (0.9+s)**2))

def Rule1_min(s,e):
	return min(A2(s),B2(s))

def Rule2_min(s,e):
	return min(A1(s),B2(s))

def Rule3_min(s,e):
	return min(A1(s),B1(s))


def COG(w,c):
    if len(w) != len(c):
        return -1
    else:
        broitel=0
        imenitel=0
        for i in range(len(w)):
            broitel+=w[i]*c[i]
            imenitel+=w[i]

        return broitel/imenitel



if __name__ == "__main__":
    t=input()
    h=input()
    w1,w2,w3 = Rule1_min(t,h),Rule2_min(t,h),Rule3_min(t,h)
    w = [w1,w2,w3]
    c = [2000,500,100]
    cog=COG(w,c)
    print cog