program info;
var n,i,j,c:longint;
    prim:array[1..200005]of boolean;
    f,g:text;
begin
  assign(f,'ciur.in');
  reset(f);
  assign(g,'ciur.out');
  rewrite(g);
  readln(f,n);
    for i:=2 to n do
      prim[i]:=true;
    i:=1;
  while i<= sqrt(n) do
   begin
    i:=i+1;
        if prim[i]= true then
          begin
            for j:=2 to n div i do
               prim[j*i]:=false;

          end;
   end;
   for i:=2 to n do
     if prim[i] then
       c:=c+1;
        writeln(g,c);
  close(f);
  close(g);
end.