from math import log2 N=int(input()) P=[int(input()) for i in range(N)] def F(n): x=0 y=0 for i in range(1,n+1): x+=0.81**i y+=0.9**i return (x**(1/2))/y #for i in range(1,1000): # print(F(i)) F_inf=0.22941573387056197 def f(n): return (F(n)-F_inf)/(F(1)-F_inf)*1200 def g(x): return 2**(x/800) def g_inv(x): return 800*log2(x) x=0 y=0 for i in range(1,N+1): x+=g(P[i-1])*(0.9**i) y+=0.9**i print(g_inv(x/y)-f(N))