while(1):
    try:
        num=list(map(int,input().split()))
        p=num[0]
        t=num[1]
        g1=num[2]
        g2=num[3]
        g3=num[4]
        gj=num[5]
        if abs(g1-g2)<=t:
            print("%.1lf"%((g1+g2)/2))
        else:
            if abs(g1-g3)<=t:
                print("%.1lf"%((g1+g3)/2))
            elif abs(g2-g3)<=t:
                print("%.1lf" % ((g2 + g3) / 2))
            else:
                print(gj)
    except:
        break