uses crt;
var n,i,j,c,z,k,d:integer;
s:real;
begin
clrscr;
write('n=');
readln(n);
s:=0;
for i:=1 to n do
begin
c:=2*i-1;
z:=c+1;
d:=c-1;
k:=z;
for j:=2 to c do
begin
d:=d+1;
k:=k+d;
z:=z+k;
end;
s:=s+c/z;
end;
write('S=',s:0:6);
readln
end.