rogram xx303;
var
i,j,s,n,k:integer;
begin
readln(n);
s:=0;
for i:=1 to n do begin
k:=-1;
for j:=1 to i do
k:=-k;
s:=s+k*i;
end;
writeln(s);
end.

输入：100
输出：-50