var i,n,sum:real
begin
sum:=0;
readln(n);
for i:=1 to n do
sum:=sum+(1/(n*(n+1)*(n+2)));
writeln(sum);
end;
var i,n,sum:real
begin
sum:=0;
readln(n);
for i:=1 to n do
sum:=sum+(1/(n*(n+1)*(n+2)));
writeln(sum);
end;