Program Ciur;

 var n, k2 : integer;
     fi, fo : text;
     r : array[1..640000] of byte;
     i, j : word;
begin
 assign(fi, 'ciur.in');
 assign(fo, 'ciur.out');
 reset(fi);
 rewrite(fo);
 readln(fi, n);
 for i:=1 to n do
  r[i]:=1;
 for i:=2 to n div 2 do
  for j:=2 to n div i do
  r[i*j]:=0;
 for i:=2 to n do
  if r[i]=1 then inc(k2);
 writeln(fo, k2);
 writeln(fo);
 close(fo);
end.