Var i,n,s:integer;
begin
readln(n); s:=0;
for i:=1 to n do
if i mod 2 = 0 then s:=s+i;
writeln('tong so chan', s);
readln;
end.
uses crt;
var n,i,s,dem:integer;
begin
clrscr;
write('nhap n:');readln(n);
s:=0; dem:=0; i:=0;
while dem<=n do
begin
if i mod 2 =0 then
begin
s:=s+i;
dem:=dem+1;
i:=i+1;
end
else i:=i+1;
end;
write(s);
readln;
end.