var a:array[1..2000000] of byte;
    n,i,j,k:longint;
    f,g:text;
    begin
    assign(f,'ciur.in');
    reset(f);
    readln(f,n);
    fillchar(a,sizeof(a),1);
    a[1]:=2;
    k:=0;
    for i:=2 to n do
    begin
      if a[i]=1 then begin j:=i;
                           k:=k+1;
                     while j<=n  do
                     begin
                     j:=j+i;
                     a[j]:=2;
                     end;
                     end;
                     end;
          assign(g,'ciur.out');
          rewrite(g);
          writeln(g,k);
          close(f);
          close(g);
          end.