{programmer:mogtaba amirzade 
url http:\\www.ifjam.com
}
p12.pas
program p12(input,output); {16:while form}
var
s:real;
k,j,n:integer;
begin
s:=1.0;
k:=1;
j:=2;
readln(n);
while j<=n do
begin
s:=s+k/j;
k:=-k;
j:=j+1;
end; {while}
writeln(s:1);
readln
end.