var a:array[1..1000000] of boolean;
    i,j,n,k:longint;
    
begin
  assign(input, 'ciur.in');
  reset(input);
  assign(output, 'ciur.out');
  rewrite(output);
  readln(N);
  for i:=1 to N do a[i]:=true;
  for i:=2 to N do
    if a[i] then
      for j:=2 to N div i do
        a[i*j]:=false;
  k:=0;
  for i:=2 to N do
    if a[i]
    then k:=k+1;
  writeln(k);  
end.