program p1;
label 1;
var
i, n, sum: integer;
prod: char;
begin
1:
write('N= ');
readln(n);
sum := 0;
i := 1;
while (i < n + 1) do
begin
sum := sum + i;
i := i + 3;
end;
writeln('Summa= ', sum);
write('Vi xotite prodoljiti? (y/n) ');
readln(prod);
if prod = 'y' then
goto 1;
readln;
end.