program ciur;
var v:array[1..20000000] of 0..1;
    i,n,j,nr:longint;

begin
  assign(input,'ciur.in'); reset(input);
  assign(output,'ciur.out'); rewrite(output);
  readln(n);
  nr:=1;
  for i:=3 to n do
    begin
      if i mod 2=0 then v[i]:=1
       else
      if (v[i]=0) then
        begin
           inc(nr);
           j:=i;
           while j<n do
             begin
               j:=j+i;
               v[j]:=1;
             end;
        end;
    end;
  writeln(nr);
  close(input); close(output);
end.