program Ciur;
var
  n,i,j,k,l:longint;
  a:array[1..20000000] of byte;
  fl:text;
begin
   assign(fl,'ciur.in');
   reset(fl);
   readln(fl,n);
   close(fl);

   for i := 1 to n do
      a[i] := 1;

  a[1] := 0;
  k := 0;
  for i := 2 to n do
     if (a[i] = 1) then
        begin
           j := 2*i;
           k := k+1;
           while j<= n do
           begin
              a[j] := 0;
              j := j+i;
           end;
     end;

  assign(fl,'ciur.out');
  rewrite(fl);
  writeln(fl,k);
  close(fl);
end.