program ChapterCal;
uses crt;

var
total, current, week : integer;

begin
	week := 1;
	writeln('Enter number of starting chapters');
	readln(current);
        clrscr;
	total := current;
	repeat
                begin
                if (week = 2) then
                begin
                	total := total + 1;
			week := 1;
		end
                else
                begin
			total := total + 1;
			current := current - 1;
			week := 2;
                end
                end
        until current = 0;
	writeln(total);
	readln();
end.