var a:array[2..2000005] of boolean;
    n,nr:longint;

procedure citire;
var f:text;
begin
	assign(f,'ciur.in');reset(f);
	readln(f,n);
	close(f);
end;

procedure ciur;
var i,j:longint;
begin
	for i:=2 to n do a[i]:=true;
	
	for i:=2 to n do if a[i] then
	begin
		inc(nr);
		for j:=2 to n div i do a[i*j]:=false;
	end;
end;

procedure afisare;
var f:text;
begin
	assign(f,'ciur.out');rewrite(f);
	writeln(f,nr);
	close(f);
end;

begin

citire;
ciur;
afisare;

end.