var
i,N,S:integer;
begin
read(N);
for i:=1 to N do
if i mod 2 = 0 then
S+=i;
writeln(S);
end.
var
i,N,S:integer;
begin
read(N);
i:=1;
while i<=N do
begin
if i mod 2 = 0 then S+=i;
i+=1;
end;
writeln(S);
end.
var
i,N,S:integer;
begin
read(N);
i:=1;
repeat
if i mod 2 = 0 then S+=i;
i+=1;
until i>N;
writeln(S);
end.