sub F{my$n=pop;
	sqrt(
		(1-0.81**$n)/0.19
	)/(1-0.9**$n)/10
}
sub f{my$n=pop;
	(F($n)-F(1e5))/(F(1)-F(1e5))*1200
}
sub g{my$X=pop;
	2**($X/800)
}
sub g_inv{my$X=pop;
	800*log($X)/log(2)
}
($n,@RPerf)=<>;
$a+=g(@RPerf[$_-1])*0.9**$_ for 1..$n;
print$-=g_inv($a/(9*(1-0.9**$n)))- f($n)