program ciur3;
 var i,n,j,nr:longint;
     ciur:array[1..2000000] of byte;
     f,g:text;
Begin
 assign(f,'ciur.in');reset(f);
 assign(g,'ciur.out');rewrite(g);
 {write('n=');readln(n);}
 read(f,n);
 for i:= 2 to n do
  if ciur[i] = 0 then begin
    nr:=nr+1;
    j:=i+i;
    while j<=n do begin
      ciur[j]:=1;
      j:=j+i;
    end;
  end;
 write(g,nr);
 close(g);close(f);
end.