var fin,fout:text;
    n,i,k:longint;
    
function prim(n:longint):boolean;
var i,r:longint;
begin 
  if (n=2) or (n=3)
  then prim:=true
  else if n mod 2=0
  then prim:=false
  else
  begin
    i:=3; r:=trunc(sqrt(n));
    while (i<=r)and(n mod i<>0) do i:=i+2;
    prim:=n mod i<>0;
  end;
end;
    
begin
  assign(fin, 'ciur.in');
  reset(fin);
  assign(fout, 'ciur.out');
  rewrite(fout);
  
  readln(fin,n);
    
  for i:=2 to n do
    if prim(i)
    then inc(k);
    
  writeln(fout,k);
  
  close(fout);
end.