__author__ = 'Damjan'
import math

def A1(s):
    if s>=60:
        return 1.0
    elif s<60:
        return 1.0/pow(math.e,(60-math.fabs(s)))
    else:
        return -1.0

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

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

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

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

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

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

def COG(w,c):
    broitel = 0
    imenitel = 0
    if len(w)!= len(c):
        return -1
    else:
        for i in range(len(w)):
            broitel+=w[i]*c[i]
            imenitel+=w[i]
    return broitel/imenitel
def C1():
    return 2000.0
def C2():
    return 500.0
def C3():
    return 100.0
if __name__ == "__main__":
    t=input()
    h=input()
    w1=Rule1_min(t,h)
    w2=Rule2_min(t,h)
    w3=Rule3_min(t,h)
    c1 = C1()
    c2 = C1()
    c3 = C3()
    w = [w1,w2,w3]
    c = [c1,c2,c3]
    print COG(w,c)