program project1;
uses math;
var y, s, n, e:real;
begin
y:=1;
s:=1;
n:=1;
e:=0.0001;
while y>e do begin
y:=1/power(2,n);
s:=s+y;
n:=n+1;
end;
writeln(s:7:5);
readln;
end.