var k,n,i,j:longint;
    ciur:array[2..2000003]of boolean;
    f:text;
begin
assign(f,'ciur.in');
reset(f);
readln(f,n);
close(f);k:=0;
for i:=2 to n do
 if not ciur[i] then
  begin
   inc(k);
   j:=i*i;
   while (j<=n)and(j>0) do
    begin
     ciur[j]:=true;
     inc(j,i)
    end;
  end;
assign(f,'ciur.out');
rewrite(f);
writeln(f,k);
close(f);
end.