program ciur;
var N, cnt,i,j:longint;
    prim:array[1..2000200] of 0..1;
    f,g:text;
begin
  assign(f,'ciur.in');
  assign(g,'ciur.out');
  reset(f);
  rewrite(g);
  readln(f,n);
  for i:=2 to n do
    prim[i]:=1;
  for i:=2 to n do
    if prim[i]=1  then
        begin
          cnt:=cnt+1;
         { write(g,i,' '); }
          j:=i;
          while j<=n do
            begin
              prim[j]:=0;
              j:=j+i;
            end;
          {for j:=i+i to n do
            prim[j]:=0;}
        end;
  {writeln(g); }
  writeln(g,cnt);
  close(f);
  close(g);
end.