program chik;
var s,i,n:integer;
begin
readln(n);
for i:=1 to n do
if(i mod 2=0)then s:=s+i;
writeln(s);
end.
program chik;
var s,i,n:integer;
begin
readln(n);
for i:=1 to n do
if(i mod 2=0)then s:=s+i;
writeln(s);
end.